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For other uses, see Portal (disambiguation).
Joel Shoop (UI / UX Design)
Portal 2 is the sequel to Portal. First hinted in the update made to Portal in March 2010 as part of the Portal ARG, it was announced on March 5, 2010 to be released in fall 2010, but was later announced on June 9, 2010 as delayed until an unspecified date in 2011. It was later said to be released on February 9, 2011. This date was again delayed to April 19.
- ATLAS and P-body
- Cave Johnson (voice only)
- Caroline (voice only)
- Doug Rattmann (scribblings only)
- Sentry Turrets
- Space Core
- Adventure Core
- Fact Core
Portal 2 is a first-person perspective puzzle game. Players take the role of Chell in the single-player campaign, as one of two robots - Atlas and P-Body in the cooperative campaign, or as a simplistic humanoid icon, nicknamed "Bendy" in community-developed puzzles. Characters can withstand limited damage but will die after sustained injury or after falling into bottomless pits or toxic waste. While most of the game takes place in modular test chambers with clearly defined entrances and exits, other parts occur in behind-the-scenes areas where the objectives are less clear.
The initial tutorial levels guide the player through the general movement controls and illustrate how to interact with the environment. The player must solve puzzles using the Aperture Science Handheld Portal Device, which can create two portals connecting two distant surfaces. Outlines of placed portals are visible through walls and other obstacles for easy location.
New testing elements include Thermal Discouragement Beams, Excursion Funnels, and Hard Light Bridges, all of which can be transmitted through portals; Aerial Faith Plates launch the player or objects through the air. The Weighted Storage Cube has been redesigned, and there are new types: Thermal Redirection Cubes, which have prismatic lenses that redirect laser beams, spherical Edgeless Safety Cubes, and Frankenturrets - cube-turret hybrids created by Wheatley after taking control of Aperture Science Enrichment Center.
Newly introduced Mobility Gels impart certain properties to surfaces or objects coated with them, themselves dispensed from pipes and transported through portals. Players can use the Propulsion Gel to cross surfaces more quickly, Repulsion Gel to bounce from a surface, and Conversion Gel to allow surfaces to accept portals. Only one type of gel can be effective on a certain surface at a time only. Some surfaces, such as grilles, cannot be coated with a gel. Cleansing Gel can block or wash away other gels, returning the surface or object to its normal state.
The game includes a two-player cooperative mode. Two players can use the same console with a split screen, or can use a separate computer or console; Microsoft Windows, macOS, and PlayStation 3 users can play with each other regardless of platform; a patch provided in late 2012 added split-screen support for Windows and macOS users under "Big Picture" mode. Both player-characters are robots that control separate portal guns and can use the other character's portals. Each player's portals are of a different color scheme, whereof one is blue and purple and the other is orange and red. A calibration chamber separates the characters to teach the players to use the communication tools and portals. Most later chambers are less structured and require players to use both sets of portals for laser or funnel redirection, launches, and other maneuvers. The game provides voice communication between players, and online players can temporarily enter a split-screen view to help coordinate actions. Players can use the ping tool to draw the other player's attention to walls or objects, start countdown timers for synchronized actions, and perform joint gestures such as waving or hugging. The game tracks which chambers each player has completed and allows players to replay chambers they have completed with new partners.
According to Valve, each of the single-player and cooperative campaigns is 2 to 2.5 times as long as the campaign in Portal, with the overall game five times as long. Portal 2`s lead writer Erik Wolpaw estimates each campaign about six hours long. Portal 2 contains in-game commentary from the game developers, writers, and artists. The commentary, accessible after completing the game once, appears on node icons scattered through the chambers.
After the success of Portal, Valve decided to make Portal 2 a standalone product, partly because of pressure from other developers within Valve who wanted to work on a Portal product. Work began almost immediately after the release of Portal. Valve committed more resources to Portal 2`s development than they had for the first game; Portal had a team of seven or eight people, but Portal 2 had a team of 30 or 40. The initial team of four was expanded as subgroups formed to devise game mechanics and to plot the story. Participants in internal review processes were inspired by what they saw to join the project. According to Erik Wolpaw, some Portal 2 developers worked on the Left 4 Dead games to help them meet milestones, but returned to Portal 2, "with extra people in tow." Kim Swift, Portal`s designer, left Valve for Airtight Games halfway through Portal 2`s development.
Project manager Erik Johnson said Valve's goal for Portal 2 was to find a way to "re-surprise" players, which he considered a "pretty terrifying" prospect. In March 2011, one month before the game's release, Valve president Gabe Newell called Portal 2 "the best game we've ever done." After Portal 2`s release, Geoff Keighley wrote that according to Newell, "Portal 2 will probably be Valve's last game with an isolated single-player experience". Keighley later stated that the use of the word "probably" suggests that "this could change." Newell said that Valve is not "giving up on single-player at all", but intends to include more social features on top of the single player experience, akin to the cooperative mode in Portal 2.
Early in its development, the development team planned to exclude portals from Portal 2. For five months, Valve focused on a gameplay mechanic called "F-STOP". Though the new mechanics prompted some positive feedback, every playtester expressed disappointment at the omission of portals. Following a report in Kotaku of some leaked aspects of the game's plot then under consideration, Newell directed the team to reconsider its plans for Portal 2, including the lack of portals.
Johnson stated that Valve's aim was not to make Portal 2 more difficult than its predecessor, but instead to produce "a game where you think your way through particular parts of the level, and feel really smart when you solve it." Portal 2 allows the player to take incremental steps to understand the game's mechanics, an approach that led to two basic types of test chamber. The first type, which Valve calls "checklisting", provides a relatively safe environment for player to experiment with a new gameplay concept; the second type combines elements in new ways to force the player to think laterally, providing challenging and rewarding puzzles. Chambers were first developed through whiteboard via isometric drawings. The developers performed a sanity check on the chamber before crafting simple levels with the Hammer level editor. Extensive play-testing ensured the solutions to each chamber were neither too obvious nor too difficult, and observed alternative solutions discovered by playtesters. Based on play-testing results, the design team retained these alternative solutions or blocked them if they were considered too easy. These versions were sent back for further play-testing to verify that the new elements did not prevent players from finding solutions; further iterations between artists and playtesters occurred until such issues were resolved. Some elements from Portal were modified to suit Portal 2; whereas players of Portal would be familiar with the game mechanics, novice players required some training, as would players of Portal for some game elements. For example, the Energy Spheres used in the first game were replaced with lasers, which provided immediate feedback and reduced the in-game training time.
The designers built several of Portal 2`s early chambers by applying decay, collapse, and overgrowth to Portal chambers to give Portal players a sense of nostalgia and a sense of time passed in the game's world. The design team replaced low resolution textures from the first game with higher-resolution, dirty textures that the new game engine could support. The middle section of the single-player campaign takes place in large in-game spaces in which most surfaces are unable to accept portals, which forces players to find creative ways to cross them. Much of the architecture in these sections was inspired by photographs of industrial complexes, including CERN, NASA, and the abandoned Soviet space program. According to writer Jay Pinkerton, in the game's final section, in which Wheatley controls the Aperture facility, "the level designers just had a blast" creating deranged chambers reflecting Wheatley's stupidity. The designers recognized that solving puzzles would mentally tire players, so they inserted occasional "experiences" to provide a respite and to advance the plot.
Portal 2 integrates a game mechanic from Tag Team's Tag: The Power of Paint: paint-like gels that impart special properties to surfaces or objects they coat. Impressed by Tag, Valve hired its creators to develop the mechanic further and only later decided to include it in Portal 2. Valve's vice-president of marketing said, "the decision to combine their tech with Portal 2 came naturally". Journalists have likened Tag to Narbacular Drop, the DigiPen student project that became Portal. The Repulsion and Propulsion Gels in Portal 2 originated in Tag. Using the third Tag gel, which allows the character to walk on any coated surface regardless of gravity, gave playtesters motion sickness. It was replaced by Conversion Gel, which integrates with the portal mechanic. The gels give the player more control over the environment, which increased the challenge for the puzzle designers. The gels are rendered using fluid dynamics routines specially developed at Valve by the former Tag Team.
Portal 2 uses advanced rendering techniques developed for Left 4 Dead 2 for rendering pools of liquid; Portal 2 combines "flowing" surface maps to mimic the motion of water with "debris flow" maps and random noise to create realistic, real-time rendering of water effects.
The cooperative gameplay originated from players' requests and from anecdotes of players working together on the same computer or console to solve the game's puzzles. Wolpaw likened this to players working together on the same computer to solve point-and-click adventure games. The cooperative campaign was also inspired by Valve's Left 4 Dead cooperative games, in which players enjoyed discussing their personal experiences with the game when they had finished playing it. While the single player campaign in Portal 2 is designed to avoid frustrating the player, the cooperative levels focus on coordination and communication, and Valve recognizes they are much more difficult than the single-player puzzles. Valve did not include timed puzzles in the single-player campaigns in Portal and Portal 2, but found that their inclusion in the cooperative mode is effective and gives players a positive feeling after they successfully plan and execute difficult maneuvers. Each puzzle chamber in the cooperative mode requires four portals to solve to prevent puzzles being solved by the actions of only one player. As soon as a playtester discovered a way to complete a puzzle with one set of portals, the level was sent back to the designers for further work. Except in a few cases, Valve designed the chambers so that both players would remain in sight of each other to promote communication and cooperation. Some of the puzzle chambers were designed asymmetrically; one player would manipulate portals and controls to allow the other player to cross the room, emphasizing that the two characters, while working together, are separate entities. The designers soon realized that the ability to tag surfaces with instructional icons for one's partner was a necessary element, since they found this to be more effective for cooperation than simple, verbal instructions.
Valve considered adding a competitive mode to Portal 2. According to Wolpaw, the mode was similar to the video game Speedball; one team would try to transport a ball from one side of the playing field to the other using portals, while the other team would attempt to stop them with their own use of portals. Matches would commence with this objective in mind, but quickly descended into chaos. Valve realized that people enjoyed solving puzzles with portals more and therefore they focused on the cooperative mode.
Erik Wolpaw, National Lampoon veteran Jay Pinkerton and Left 4 Dead writer Chet Faliszek wrote the game's script. Wolpaw and Pinkerton wrote the single-player campaign story, while Faliszek wrote GLaDOS's lines for the cooperative campaign. The game has 13,000 lines of dialogue. The writers felt they needed to create a larger story for a stand-alone title, and wanted the game to "feel relatively intimate", and avoided adding too many new characters. They considered expanding the "sterility and dryness" of Portal and adding more comedy to the script. Wolpaw said that while some developers have been moving towards art games, no one had made a comedic video game. The game's story development was tightly coordinated with the gameplay development and testing.
The developers of Portal 2 at first envisioned it a prequel to Portal set in the 1950s, long before GLaDOS took over the Aperture Science facility, with events set in motion when Aperture CEO Cave Johnson becomes trapped within a computer. Johnson would have led an army of robots, which would battle against the player to rise to power within Aperture. In June 2008, based on information from a casting call website and leaked script samples, Kotaku reported that Valve was seeking voice actors to play Johnson, named him as an AI and identified the game as a prequel. Valve attributed this leak to an "overeager agent". Following negative playtester feedback about the omission of Chell and GLaDOS, Portal 2 was re-conceived as a sequel. The team returned to the idea of exploring parts of the facility from Aperture's early days, and reincorporated Johnson through a series of recordings.
The writers originally conceived several premature joke game endings if the player performed certain actions, but these required too much development effort for little payback and were scrapped. One of these joke endings was triggered by shooting a portal onto the moon's surface, after which the player's character would die from asphyxiation over a closing song, but the idea of creating a portal on the moon was incorporated into the game's final ending. The writers planned that Chell would say a single word during the ending, but this was not considered funny enough. In an early version of the script, Chell finds a lost "tribe" of turrets looking for their leader, a huge "Animal King" turret which can be seen in in-game videos of the retail product. As a reward, the Animal King would have married Chell to a turret, which would have followed Chell around the game without visible movement. The cooperative campaign was planned to feature a more detailed storyline, in which GLaDOS would send two robots to discover human artifacts, such as a comic based on a pastiche of Garfield. The writers hoped to use this idea to make the robots human-like for testing purposes, but recognized that unlike the captive audience of the single-player campaign, the two players in cooperative mode may simply talk over the story, and thus the story was condensed into very basic elements.
Wolpaw said that while many story elements of Portal are revisited in Portal 2, he avoided some of the memes—such as the frequently repeated "the cake is a lie". He said, "if you thought you were sick of the memes, I was sick of it way ahead of you". Wolpaw "couldn't resist putting in just one" cake joke. The writers did not try to predict or write new memes, and Wolpaw said, "you can't really plan for [dialogue to become a meme] because if you do it probably seems weird and forced". Portal 2 produced its own memes, including a space-obsessed personality core. Valve later created a Space Core modification for the game The Elder Scrolls V: Skyrim, and the Space Core also appeared as a laser-based engraving on a panel manufactured by NASA for the International Space Station.
The writers saw Aperture Science itself as a character. It is depicted as a "living, breathing place", and "a science company that's gone mad with science." In the Lab Rat comic, the facility is described as a "beautiful and terrible" place, "a metastasized amalgam of add-ons, additions and appropriations. Building itself out of itself."
Richard McCormick of PlayStation 3 Magazine identified several elements of Portal 2`s story that reference the myth of Prometheus; McCormick wrote that GLaDOS a personification of Prometheus, who grants knowledge to humanity—in the form of the portal gun—and is then punished by being bound to a rock, pecked at by birds, and is cast into the pits of Tartarus. McCormick also likens Wheatley to Prometheus' foolish brother Epimetheus. Within the game, a sentry gun makes reference to the Prometheus myth, the word "Tartarus" is visible on the supporting columns in the depths of Aperture Science, and a portrait of Cave and Caroline also shows Aeschylus, the presumed author of Prometheus Bound.
 Character design
Though Portal 2 introduced some new characters, the writers wanted to maintain the one-on-one relationships between each character and the player-character. Valve explored the possibility of introducing a new protagonist for Portal 2. The playtesters accepted playing as a different character for the first part of the game, but they became disoriented when GLaDOS did not recognize them. The writers returned to using Chell, the protagonist of Portal. Valve artists experimented with Chell's attire, and considered changing her (ambiguous) nationality. They returned to the orange "dehumanizing" jumpsuit from Portal with the top tied around Chell's waist to enhance her freedom of movement and help her "stand out more as an individual". PSM3 called the new look "controversially sexy". As in the first game, Chell's facial appearance is based on that of voice actress Alésia Glidewell. Chell continues her role as a silent observer, as the straight man in response to the insanity around her and refuses to give her antagonists any satisfaction.
As part of her character arc, the plot moves GLaDOS from her anger with Chell for her actions in Portal, which Wolpaw said "was going to get old pretty quick", to an internal struggle. The reuse of McLain's voice led to the creation of a backstory and subplot about GLaDOS's creation. The writers panicked when they realized that their plans to have Chell and GLaDOS play off each other would only work if both players spoke. To remedy this, they created the Caroline subplot to give GLaDOS an external situation to deal with and to drive the story during the middle act of the game.
The writers considered introducing about six personality cores stored in portable spheres, whose main function would be story advancement. They planned cores based on Morgan Freeman's character Red from The Shawshank Redemption and Quint from Jaws, among others. Ultimately they decided to concentrate on a single core, Wheatley, recycling two of the rejected cores in the final boss fight. Karen Prell led the animation team for Wheatley and the other personality cores.
Pictures of Cave Johnson, based on the face of lead animator Bill Fletcher, appear throughout Portal 2. Though comparisons have been made between Johnson and Andrew Ryan, the wealthy industrialist who created the fictional underwater city of Rapture in BioShock, Wolpaw says the writers did not consider this character while creating Johnson. The two robotic characters provide some amusing death scenes in the cooperative mode, such as struggling while being crushed by a lowering ceiling. The artists thought the look of the robots would help tell the story, and the fact that they are holding hands emphasizes the cooperative mode. "Expressive noises" and mannerisms are used in place of distinguishable dialogue, and the robotic characters were designed as a double-act, similar to Laurel and Hardy.
 Voice cast
GLaDOS returns from Portal as a major character and the game's antagonist, and is voiced by Ellen McLain. The writers found that they needed another character to play off Johnson, but did not want to hire another voice actor. Having already recruited McLain to play GLaDOS, they asked her to provide the voice for Caroline, Cave Johnson's assistant. Wheatley is voiced by Stephen Merchant; early demonstrations at trade shows used the voice of Valve animator Richard Lord. The writers wrote Wheatley's lines with Merchant in mind, citing his unique "vocal silhouette" and his ability to ad lib in a "frantic" manner. They had assumed that Merchant would be unavailable and contacted The IT Crowd`s writer Graham Linehan to try to get Richard Ayoade, but then discovered that Merchant was interested. Merchant spent around sixteen hours recording lines and was given freedom to improvise.
J.K. Simmons voices Cave Johnson, Aperture Science's founder and CEO. Simmons's selection helped to solidify the character's development. The robots' voices were provided by Dee Bradley Baker, who had performed similar robotic voices for the Star Wars: The Clone Wars media.
In the cooperative campaign, a separate story involves two robotic characters and GLaDOS. The designers initially planned to use Chell and a new human character called "Mel". GLaDOS' dialogue would play off the humans' "image issues", and this aspect was retained after the designers switched to using robots. GLaDOS seems troubled by the robots' cooperation, and tries to aggravate their relationship through psychological tactics, such as praising one robot over the other. Valve initially considered having GLaDOS deliver separate lines to each player, but they found this to be a significant effort for minimal benefit. The writers also tried adding lines for GLaDOS that would encourage the players to compete against each other for rewards, such as meaningless points, but playtesters did not respond well. Faliszek said that in cooperative games, it can be difficult to deliver key dialogue or in-game events to players, who may not be looking in the right direction at the right time. Instead, using their experience from previous games, Faliszek and Wolpaw kept the story and key comedic lines short, and repeated them frequently.
In January 2008, Valve spokesman Doug Lombardi told Eurogamer, "There'll be more Portal, for sure", and Portal designer Kim Swift confirmed that work on Portal 2 would begin the following month. Swift said multiplayer Portal was technically possible, but that it was "less fun than you'd think."
Portal 2 was officially announced on March 5, 2010 via Game Informer. Events during the preceding week foreshadowed the announcement. On March 1, Valve released a patch for Portal that included a new achievement, "Transmission Received", requiring the player to manipulate in-game radios. This revealed new sound effects that became part of an alternate reality game. The new effects included Morse code strings that suggested GLaDOS was rebooting and SSTV images from a grainy Aperture Science video. The images included hints to a BBS phone number that, when accessed, provided a large number of ASCII-based images relating to Portal and segments of Aperture Science documents. Many of these ASCII pictures were later published in the Game Informer reveal of the title. New ASCII images continued to appear on the BBS after the official announcement. Background on the ARG is embedded in additional SSTV images found in a hidden room in Portal 2. Valve's Adam Foster came up with the idea for the ARG, tying it to the Game Informer reveal, and he provided his own home phone line to run the BBS software on, as Valve's offices at the time were too modern to support the protocol. Foster estimates the ARG cost less than $100 to run.
A second Portal patch released on March 3 altered the game's ending sequence to show Chell being pulled back into the Aperture Facility by the Party Escort Bot. Gaming journalists speculated that an announcement of Portal 2 was imminent. On March 5, Game Informer announced Portal 2`s official release on the cover of its April issue. During the following week, Gabe Newell's speech accepting the Pioneer Award at the Game Developers Conference 2010 ended with a fake blue screen of death appearing on a screen behind him with a message purported to be from GLaDOS which hinted of further Portal 2 news at the upcoming E3 2010. Two weeks before the E3, game journalists received a cryptic e-mail, worded as a press release from Aperture Science, hinting that the presentation on Portal 2 would be replaced with "a surprise" jointly hosted by Aperture Science and Valve. This prompted speculation that the surprise would be the announcement of Half-Life 2: Episode Three, but Valve confirmed that it would be about Portal 2. The surprise was the announcement of Portal 2 on PlayStation 3.
 Marketing and release
The March 2010 announcement said that Portal 2 would be released in late 2010.</ref> In August 2010, Valve postponed the release to February 2011, with a Steam release date of February 9, to allow it to complete changes to the game's dialogue, to fill and connect about sixty test chambers, and to finish refinements to the gel gameplay mechanic. Valve announced a further delay in November 2010, and gave a worldwide release date through retail and online channels of April 18, 2011. Wolpaw stated that this eight-week delay was used to expand the game's content before reaching an internal milestone called a "content lock", after which no further content could be added. The remaining development work involved debugging. Newell allowed the delay considering the added benefits of the new content, because he thought the company would not lose any commercial opportunities because of it. On February 18, 2011, Newell confirmed that Valve had completed the development work on Portal 2 and that they were "waiting for final approvals and to get the discs manufactured". Portal 2 was the first Valve product simultaneously released for Windows and Mac OS X computers through the Steam platform. Retail copies for all platforms were distributed by Electronic Arts.
On April 1, 2011, Valve released another alternate reality game called the Potato Sack. Players tried to solve the multi-tiered puzzle, coordinating efforts through web sites and chat rooms. Some journalists believed the game denoted the release of Portal 2 on April 15, 2011, instead of the target release date of April 19, 2011. On April 15, the players discovered "GLaDOS@Home", a distributed computing spoof that encouraged participants to play the games to unlock Portal 2 early. Once the puzzles were solved, Portal 2 was unlocked about ten hours before its planned release.
Valve created a series of television commercials to promote Portal 2. Valve had worked with advertising agencies in the past, but Lombardi found the advertisements created had shown little ingenuity. Valve's Doug Lombardi had been disappointed by "Copycat treatments. Cliché treatments. Treatments that reveal the agency wasn't listening in the initial meeting." Using viewer feedback, Valve tailored the ad content until they were satisfied with the results. The ads took eight weeks to complete. Valve also developed online promotional videos featuring J. K. Simmons narrating as Cave Johnson, to promote new elements of Portal 2`s gameplay. These videos were part of a larger effort described by Newell as a "documentary-style investment opportunity" for Portal 2. An earlier video released on February 14, 2011 promoted the cooperative aspect of Portal 2 as a St.Valentine's gift and "lit up our preorders, our buzz, all the metrics that are used and collected by publishers and retailers". Lombardi said the videos "dwarfed the demos and interviews we did". Valve also offered Portal 2-themed merchandise, such as posters, drinking glasses, and t-shirts.
 Use in education
Several critics wrote that Portal 2 excels in teaching the player to solve puzzles; in a review for the New York Times, Seth Schiesel wrote, "Somewhere out there an innovative, dynamic high school physics teacher will use Portal 2 as the linchpin of an entire series of lessons and will immediately become the most important science teacher those lucky students have ever had." Mathematics and science teachers wrote e-mails to Valve to tell them how they had included Portal in their classroom lessons as part of a project to promote the "gamification of learning". Portal developers Joshua Weier and Yassr Malaika led a team within Valve to explore ways of using Portal 2 for education. This led to the development of Puzzle Maker, a level editor for Portal 2 players, built from the professional tools used to develop the game. Weier and Malaika did not want to design curricula themselves, but wanted to provide educators with tools for creating lesson plans. Hammer, the only tool freely available before the release of the built-in level editor in 2012, was difficult for educators to learn and understand. Valve gave Puzzle Maker an easy-to-learn interface and the ability to share puzzles and lesson plans. The tools were developed with a mathematics teacher and her students. This formed the basis of a new "Steam for Schools" initiative launched in June 2012, under which educators could acquire Portal 2 and the Puzzle Maker software free of charge for classroom use through its "Teach with Portals" program. As of November 2012, Valve estimates that over 2,500 educators are using the "Teach with Portals" software within their lesson plans.
Portal 2 was a strong favorite of gaming journalists during closed-door previews at the E3 2010 convention. The Game Critics Awards, selected by journalists and critics, awarded Portal 2 the title of Best PC Game and Best Action/Adventure Game, and nominated the game for Best of Show and Best Console Game. IGN named Portal 2 as its Best of E3 for PC, Xbox 360, and PlayStation 3 systems and Best Puzzle Game, and nominated it for Best Overall Game. Gamespy named Portal 2 the Best Overall Game and Best Puzzle Game of E3. Portal 2 won the 2010 Spike Video Game Award for "Most Anticipated Game for 2011".
Portal 2 received universal acclaim from reviewers on its release, and received an average score of 95 out of 100 according to review aggregator Metacritic, and between the different platform versions was ranked as the third- to fifth-highest rated game by the aggregator throughout 2011. Several reviewers identified Portal 2 as an early contender for "Game of the Year", while others called it one of the best games of all time. Upon release, the game was widely considered to be as good as or better than the original. Eurogamer's Oli Welsh said that the game avoids the normal pitfalls that developers introduce in sequels, stating that "Portal is perfect. Portal 2 is not. It's something better than that." Gus Mastrapa of the A.V. Club wrote that with Portal 2, Valve had alleviated any doubts that "Portal could be expanded into a big, narrative experience with all the bells and whistles of a mainstream gaming hit". IGN's Charles Onyett wrote that the sequel "makes the original look like the prototype it was" by expanding the game in gameplay and story.
Most reviewers praised the writing and voice acting in the game. Entertainment Weekly`s Dan Stapleton of PC Gamer was able to predict many of the plot twists within Portal 2`s story but "still looked forward to witnessing exactly how the characters would react"; he praised the development of the characters, as "their charm makes what would otherwise be an empty and lifeless world feel boisterous and alive". The characters were well received. Oynett wrote that Merchant's "obvious enthusiasm for the role benefits the game" and that the "consistently clever writing perfectly complements the onscreen action". Game Informer`s Adam Biessener considered Johnson to be an even better character than GLaDOS, and praised the game's "pitch-perfect delivery" and "brilliant comedic timing". In contrast, Peter Bright of Ars Technica wrote that compared to the loneliness and despair he felt while playing the first game, the characters, Wheatley and GLaDOS, lost some of this feeling and "the inane babble served only to disrupt the mood".
Portal 2`s additional gameplay elements, like Hard Light Bridges, Thermal Discouragement Beams, and the Mobility Gels, were praised as appropriate additions to the game. Reviewers were pleased with the difficulty of the puzzles throughout the game, which appeared visually complicated at first but had uncomplicated solutions. Time`s Evan Narcisse said that he feared the addition of new gameplay elements would "dilute the purity of the experience, but everything's still executed with Valve's high level of charm and panache." Tom Hoggins of The Telegraph praised the manner with which these elements were introduced through a "brilliant learning curve of direction, rather than instruction", and considered it a "design ethos that is supremely generous, but dealt with marvellous economy". Chris Kohler of Wired wrote that the game's puzzles "never require excessively complicated solutions", and that much of the puzzle solving is "filled with moments that will have you slapping your forehead and thinking, 'Oh my God, I’m such an idiot - why didn’t I see that before?'. Stapleton was not as pleased with the gel additions as with the other new mechanics, calling it "difficult to control". He felt that they have "only a couple of uses at most". Bright felt that Portal 2 was easier than its predecessor, in part that he felt much of the game was effectively tutorials for the new gameplay additions, requiring "careful use of the tools provided", leaving him with the impression that "the game was on rails".
The cooperative puzzle solving aspect was highlighted as a valuable addition to the game. Welsh called the cooperative mode "one of the most satisfying and genuinely collaborative gaming experiences you can have with a friend". Onyett wrote, "Valve knows how a good co-operative mode requires a game design that doesn't simply encourage but requires you to work together. In Portal 2, communication is vital to success". Several reviewers praised the non-verbal cues that players could initiate to work with their partners. Portal 2 was praised for the amount of detail in its design, sound, and music. Nelson credited the "sheer amount of detail" put into the game's world, and wrote, "it all feels very real and natural with brief moments where you're simply sucked into this world". Onyett was impressed with the amount of visual details and capabilities Valve achieved from their Source game engine and that the added details and animations of the levels "consistently serv[ed] not only to entertain the eye but to expand our understanding of the game's characters". Hoggins wrote that the game's world reacted to the player-character Chell's presence "in a startlingly organic way", and praised Valve's design as "an achievement of world-building that compares favourably with BioShock`s underwater city of Rapture".
Some reviewers said that the second act of the game, taking place in the less-structured portion of the old Aperture facilities, may be confusing to some players. Young wrote that in the second act, the game "cranks up the difficulty level at a speed that may dishearten casual gamers", and said that particularly when traveling between chambers, he had "absolutely no idea where I was supposed to head next". Kohler wrote that while the player can explore the abandoned areas of Aperture, "none of it ever does anything - it’s just a lot of sterile, duplicated, non-interactive environments". Watters wrote that the loading time between the game's levels, in contrast to earlier Valve games, are "long enough to make you take notice and wish they were shorter". Watters also said it was unfortunate that the game lacks "stand-alone test chambers and leaderboards ... but even so, Portal 2 is not light on content" without these. Welsh said that the attempt to recapture the spirit of the song "Still Alive" at the end credits of Portal 2 "was a mistake". Ben "Yahtzee" Croshaw wrote in his Extra Punctuation column that, while Portal 2 was a "very good game," it unnecessarily retconned portions of the origin game's story, and did not really further the game's concept. However, this criticism was directed solely at the campaign, and he stated that he found the game's co-op to be "much more appealing and much more within the spirit of the original."
On April 20, 2011, it was reported that customers had launched a protest against perceived shortcomings of Portal 2. Users complained that the game was too short - some said it is only four hours long, about the existence of paid, downloadable content for some versions at launch, and that the Windows and macOS versions were ports of the console version. Other journalists countered that the quality of the graphics on the Windows and macOS versions did not suggest a simple console port. Stephen Totilo of Kokatu.com wrote that the game lasted nine hours and that the downloadable content consisted purely of cosmetic add-ons. Some journalists said that the minimal impact of The Potato Sack alternative reality game on the early release of Portal 2 may be influencing the user scores.
Portal 2 won the title of "Ultimate Game of the Year" at the 2011 Golden Joystick Awards, and ranked second place on Time's "Top 10 Video Games of 2011". Gamasutra, IGN, Eurogamer, Kotaku, the Associated Press, and The Mirror listed Portal 2 as their top video game of 2011. The game received twelve nominations including "Game of the Year" for the 2011 Spike Video Game Awards, where it was the most-nominated title, and won for "Best PC Game", "Best Male Performance" for Stephen Merchant, "Best Female Performance" for Ellen McLain, "Best Downloadable Content", and "Best Multiplayer Game". The title was nominated for five Game Developers Choice Awards for 2011, including "Game of the Year", and won in the "Best Narrative", "Best Audio" and "Best Game Design" categories. It was nominated for ten Interactive Achievement Awards, including "Game of the Year", from the Academy of Interactive Arts & Sciences, and won the awards for "Outstanding Achievement in Connectivity", "Outstanding Achievement in Original Music Composition", and "Outstanding Character Performance" for Wheatley. Portal 2 was nominated for six BAFTA video game award categories, and won in the "Best Game", "Best Story" and "Best Design" categories. The Game Audio Network Guild awarded the game for "Best Dialog", "Best Interactive Score", and "Best Original Vocal – Pop" (for "Want You Gone"). In the inaugural New York Videogame Critics Circle Awards, Portal 2 was given the top honors for best writing and best acting. The Perpetual Testing Initiative add-on was awarded the 2012 Golden Joystick for "Best Use of DLC".
Based on sales data from Amazon.com, Portal 2 was the best-selling game in the United States in the first week of its release, but was overtaken by Mortal Kombat in its second week. According to NPD Group, Portal 2 was the second-best selling game in the U.S. in April 2011, at 637,000 copies, and the fourth-best selling in May. However, NPD does not include sales on Valve's Steam platform. Portal 2 was the best selling game in the U.K. in the first week of its release, the first number-one for a Valve game. It retained the top spot during its second week.
Portal 2 was released a few days before the PlayStation Network outage. Gamasutra analyst Matt Matthews said that, based on NPD Group data, the outage "did not seriously affect retail sales of software", but some developers did report drops in sales. ShopToNews analyst Joe Anderson expected that the effect of the outage on UK sales of Portal 2 would be mild. On June 22, Newell announced that Portal 2 had sold 3 million copies. As of July 2011, Electronic Arts stated that more than 2 million copies of Portal 2 have been sold by retailers worldwide. In an August 2011 interview, Newell stated that "Portal 2 did better on the PC than it did on the consoles". Upon release of the Perpetual Testing Initiative in May 2012, Newell stated that Portal 2 had shipped more than 4 million units, with the personal computer versions outselling the console versions. Overall, Portal and Portal 2 had together shipped more than 8 million units.
 Downloadable content
 Portal 2 Sixense MotionPack DLC
The Portal 2 Sixense MotionPack DLC is a level pack that was made available for those who purchased the Razer Hydra motion controller. It consists of six normal Test Chambers and seven advanced Chambers. With the DLC installed, the ASHPD gains several new abilities. The new features work in both the extra levels and the main campaign, but are disabled in the co-op campaign.
 Peer Review
Peer Review is a free DLC released on October 4, 2011, expanding upon the co-op side of the game.
 Perpetual Testing Initiative
The Perpetual Testing Initiative is a free DLC for PC and Mac, released on May 8, 2012, adding in a level editor, for both single-player and co-op game modes, and a story arc using player-made maps.
 Achievements and trophies
Portal 2 has 51 PC achievements, 50 Xbox 360 achievements with a total of 1000 Gamerscore points, and 51 trophies; 42 bronze trophies, 5 silver trophies, 3 gold trophies and 1 platinum trophy.
The Portal 2 soundtrack was composed by Mike Morasky, with the exception of the songs "Want You Gone" composed by Jonathan Coulton, "Offering," composed by Larry Stephens, an arrangement of Little Prelude in C Minor, BWV 934 by Johann Sebastian Bach, and "Exile Vilify," composed by The National.
 Concept box art
 Menu background videos
 Loading screens
- ↑ Eurogamer - "Portal 2 due out this Christmas"
- ↑ Portal 2 at E3 on YouTube
- ↑ http://designshoop.com/
- ↑ Game Informer, April 2010 issue
- ↑ Portal 2 Announced - March 5, 2010 - on Steampowered.com
- ↑ Portal 2 Delayed to 2011 on IGN
- ↑ Gamescom: Portal 2 release date confirmed on ComputerAndVideoGames.com
- ↑ Portal 2 spawning on April 21 in Australia
- ↑ Video: Making Portal 2, the sequel to a game that didn't need one. Gamasutra (2012-07-17). Retrieved on 2012-07-17.
- ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 Remo, Chris (2010-09-20). Synthesizing Portal 2. Gamasutra. Retrieved on 2010-09-20.
- ↑ Larchuk, Travis (2011-04-19). Portal 2: A Student Video Game Project, All Grown Up. NPR. Retrieved on 2011-06-18.
- ↑ 12.0 12.1 Crossley, Rob (2011-05-10). Valve on Portal 2. Develop. Retrieved on 2011-05-11.
- ↑ Remo, Chris (2009-12-07). Portal Designer Kim Swift Leaves Valve For Dark Void Dev. Gamasutra. Retrieved on 2010-07-09.
- ↑ 14.0 14.1 14.2 Stewart, Keith (2010-06-18). E3 2010: Portal 2 preview. The Guardian. Retrieved on 2010-06-21.
- ↑ Leone, Matt (2010-03-11). Gabe Newell: Portal 2 is "The Best Game We've Ever Done". 1UP.com. Retrieved on 2010-03-12.
- ↑ 16.0 16.1 16.2 16.3 16.4 16.5 16.6 16.7 16.8 16.9 The Final Hours of Portal 2
- ↑ Keighley, Geoff. The Final Hours of Portal 2 blog is live. Retrieved on 2011-06-18.
- ↑ Nunneley, Stephany (2011-05-07). Valve’s not "giving up on single-player at all," plans to add more social features to titles. VG247.
- ↑ 19.0 19.1 Alexander, Leigh (2011-05-06). Valve's Wolpaw Offers Behind-The-Scenes Peek Into Portal 2. Gamasutra. Retrieved on 2011-05-06.
- ↑ 20.0 20.1 20.2 Reeves, Ben (2010-03-17). Thinking With Portals: Making a Portal 2 Test Chamber. Game Informer. Retrieved on 2010-03-17.
- ↑ 21.0 21.1 Curtis, Tom (2012-03-08). GDC 2012: Portal 2: Making a sequel to a 'perfect' game. Gamasutra. Retrieved on 2012-03-08.
- ↑ 22.0 22.1 22.2 Portal 2 developer commentary
- ↑ 23.0 23.1 Ohannessian, Kevin (2011-04-27). Portal 2's Creators On Crafting Games Through Experiential Stories. Fast Company. Retrieved on 2011-04-27.
- ↑ Yang, Robert (2012-12-06). Specially Level With Me, Adam Foster – Part Two. Rock Paper Shotgun. Retrieved on 2012-12-06.
- ↑ Walker, John (2011-04-27). Valve On Portal 2: Spoiler Interview Part One. Rock Paper Shotgun. Retrieved on 2011-04-27.
- ↑ Walker, John (2011-04-28). Valve on Portal 2: Spoiler Interview Part Two. Rock Paper Shotgun. Retrieved on 2011-04-28.
- ↑ 27.0 27.1 27.2 Kao, Ryan (2010-09-04). Portal 2: A Look at the Hotly Anticipated Videogame. Wall Street Journal. Retrieved on 2010-09-04.
- ↑ Leahy, Brian (2010-03-08). Valve Hires DigiPen Team; Seemingly for Portal 2. Shacknews. Retrieved on 2010-03-08.
- ↑ Ryckert, Dan (2010-03-08). From Narbacular Drop To Portal. Game Informer. Retrieved on 2010-03-08.
- ↑ Gaskill, Jake (2010-06-18). E3 2010: Portal 2 Preview. G4TV. Retrieved on 2010-06-19.
- ↑ 31.0 31.1 Saltzmann, Marc (2011-04-14). Five things you didn't know about 'Portal 2'. USA Today. Retrieved on 2011-04-14.
- ↑ 32.0 32.1 32.2 32.3 Braga, Matt (2011-04-19). Q&A with Portal 2 writers Erik Wolpaw and Jay Pinkerton. National Post. Retrieved on 2011-04-20.
- ↑ Vlachos, Alex (2010-07-28). Water Flow in Portal 2. Retrieved on 2010-08-10.
- ↑ 34.0 34.1 Portal 2 influenced by Left 4 Dead – Valve. Computer and Video Games (2011-02-11). Retrieved on 2011-02-11.
- ↑ 35.0 35.1 35.2 Grant, Christopher (2010-06-21). Preview: Portal 2 (co-op). Joystiq. Retrieved on 2010-06-21.
- ↑ 36.0 36.1 36.2 36.3 Francis, Tom (2010-09-10). Interview: Valve on their insane Portal 2 ideas. PC World. Retrieved on 2010-09-10.
- ↑ Welsh, Oli (2012-03-08). The Portal 2 that never was. Eurogamer. Retrieved on 2013-10-08.
- ↑ Watts, Steve (2010-08-26). Valve Cut Portal 2 Competitive Multiplayer. 1UP.com. Retrieved on 2010-08-26.
- ↑ 39.0 39.1 39.2 39.3 Welch, Oli (2011-04-25). Portal 2: "Let's make Caddyshack". Eurogamer. Retrieved on 2011-04-25.
- ↑ Meer, Alec (2011-01-14). 13,000 Lines of Chat in Portal 2. Rock Paper Shotgun. Retrieved on 2011-01-14.
- ↑ de Matos, Xav (2011-03-21). Interview: Portal 2 project lead Joshua Weier and writer Erik Wolpaw. Shacknews. Retrieved on 2011-03-21.
- ↑ 42.0 42.1 Turi, Tim (2012-09-01). Chell Almost Married A Turret In Portal 2. Game Informer. Retrieved on 2012-09-06.
- ↑ Tolito, Stephen (2011-04-21). Portal 2 Wasn’t Going to Include Portals, According To New iPad App. Kotaku. Retrieved on 2011-05-06.
- ↑ Plunkett, Luke (2008-06-10). Casting call reveals Portal 2 details. Kotaku. Retrieved on 2008-07-18.
- ↑ Plunkett, Luke (2008-06-10). More details on Portal 2's bad guy. Kotaku. Retrieved on 2008-07-18.
- ↑ 46.0 46.1 Welsh, Oli (2012-03-08). The Portal 2 that never was. Eurogamer. Retrieved on 2012-03-08.
- ↑ Remo, Chris (2010-06-18). Portal 2's Wolpaw: 'I Do Not Want To Resurrect A Three-Year-Old Meme'. Gamasutra. Retrieved on 2010-06-18.
- ↑ 48.0 48.1 48.2 48.3 48.4 48.5 Brown, David (2011-03-04). Portal 2 developer interview: Chet Falisek and Erik Wolpaw. The Daily Telegraph. Retrieved on 2011-03-04.
- ↑ Arendt, Susan (2011-03-14). Portal 2's Writer Didn't Try to Reinvent the Cake. The Escapist. Retrieved on 2011-03-14.
- ↑ Grayson, Nathan (2012-02-07). Impressions: Skyrim's Portal 2 Mod. Gamespy. Retrieved on 2012-02-07.
- ↑ Phillips, Tom (2012-07-22). NASA launches Portal 2 character into orbit. Eurogamer. Retrieved on 2012-07-22.
- ↑ Griliopoulos, Dan (2011-03-28). Portal 2: Test Subjects. IGN. Retrieved on 2011-03-28.
- ↑ McCormick, Richard (2011-07-17). 10 incredible Portal 2 secrets you might have missed. PlayStation 3 Magazine. Retrieved on 2011-07-17.
- ↑ 54.0 54.1 54.2 54.3 Stanton, Rich (2011-04-26). Erik Wolpaw on Portal 2’s ending: "the (spoiler) is probably lurking out there somewhere". PC Gamer. Retrieved on 2011-04-26.
- ↑ Hillier, Brenna (2011-03-14). Wolpaw: Players Don't Care About Portal's Chell. VG24/7. Retrieved on 2011-06-20.
- ↑ 56.0 56.1 Reeves, Ben (2010-03-22). Redesigning Portal: Valve's Artist Speaks. Game Informer. Retrieved on 2010-03-22.
- ↑ McWheator, Michael (2011-02-23). The New Look For Portal 2's Heroine Explained. Kotaku. Retrieved on 2011-02-23.
- ↑ 58.0 58.1 Meet the real-life Chell from Portal 2. Computer and Video Games (2011-03-29). Retrieved on 2011-04-20.
- ↑ Goldman, Tom (2011-05-07). Valve: Portal's Chell is Silent Because It's Funnier. The Escapist. Retrieved on 2011-05-22.
- ↑ Sinclair, Brendan (2011-10-12). Writing Valve's silent protagonists. Gamespot. Retrieved on 2011-10-12.
- ↑ Sheffield, Brandon (2010-11-08). Rewarding The Players: Valve On Portal 2. Gamasutra. Retrieved on 2010-11-10.
- ↑ 62.0 62.1 Navarro, Alex (2011-05-06). 'So, Here's Something Pretentious!' – Anecdotes and Thoughts from Erik Wolpaw's Portal 2 Discussion at the NYU Game Center. Giant Bomb. Retrieved on 2011-05-06.
- ↑ Minkley, Johnny (2011-05-09). Being Nathan Drake – Interview. Eurogamer. Retrieved on 2011-05-09.
- ↑ 64.0 64.1 Johnson, Stephen (2010-09-03). PAX Prime 2010: Portal 2 Co-Op Hands-On Impressions. G4 TV. Retrieved on 2010-09-03.
- ↑ Donlan, Christian (2011-02-04). Portal 2 Hands-on. Eurogamer. Retrieved on 2011-02-04.
- ↑ Ramadge, Andrew (2011-02-21). GLaDOS, the greatest video game villain of all time, is back for more cake and chaos in Portal 2. News.com.au. Retrieved on 2011-03-23.
- ↑ Mastrapa, Gus (2010-06-16). Portal 2 Gains a Talkative Companion. Wired. Retrieved on 2010-06-16.
- ↑ Kollar, Phil (2010-08-18). Portal 2 Has A Release Date And A New Voice Actor. Game Informer. Retrieved on 2010-08-18.
- ↑ Krantzl, Justin (2011-04-19). Portal 2 releases – Unreview, uninterview, unstudiovisit. VG247. Retrieved on 2011-04-20.
- ↑ Miller, Greg (2011-03-11). PAX: Portal 2 Nabs J. K. Simmons. IGN. Retrieved on 2011-03-11.
- ↑ Portal 2 Collector's Edition Guide
- ↑ Maiberg, Emanuel (2011-01-21). Portal 2 preview. Gamepro. Retrieved on 2011-01-21.
- ↑ Purchese, Rob (2008-01-31). More Portal for sure – Valve. Eurogamer. Retrieved on 2008-01-30.
- ↑ Faylor, Chris (2008-02-23). GDC 08: Portal Creators on Writing, Multiplayer, Government Interrogation Techniques. Shacknews. Retrieved on 2008-02-23.
- ↑ Wawro, Alex (2010-04-26). Anatomy of an Alternate-Reality Game. GamePro. Retrieved on 2010-05-13.
- ↑ Portal Patch Adds Morse Code, Achievement – Portal 2 Speculation Begins (Updated). Shacknews (2010-03-01). Retrieved on 2010-03-02.
- ↑ Fletcher, JC (2011-04-20). Portal 2 Easter egg: Valve never meta-ARG it didn't like. Joystiq. Retrieved on 2011-04-20.
- ↑ Purchase, Robert (2013-06-07). The first anyone had seen publicly of Portal 2 was relayed over this modem from 1987 from my kitchen. Eurogamer. Retrieved on 2013-06-07.
- ↑ Foster, Adam (2013-06-18). Alternate Reality Game puzzle design. Gamasutra. Retrieved on 2013-06-18.
- ↑ Faylor, Chris (2010-03-03). Portal Mystery Deepens with Second Update. Shacknews. Retrieved on 2010-03-03.
- ↑ Mastrapa, Gus (2010-03-02). Geeky Clues Suggest Portal Sequel Is Coming. Wired. Retrieved on 2010-03-02.
- ↑ Gaskill, Jake (2010-03-03). Rumor: Valve To Make Portal 2 Announcement During GDC 2010. X-Play. Retrieved on 2010-03-03.
- ↑ Webster, Andrew (2010-03-05). Portal 2 is official, first image inside. Retrieved on 2010-03-05.
- ↑ Plunkett, Luke (2010-03-11). Portal 2 Hijacks Blue Screen of Death At GDC Awards. Kotaku. Retrieved on 2010-03-12.
- ↑ Purchase, Robert (2010-06-02). E3 Portal 2 event replaced by "surprise". Eurogamer. Retrieved on 2010-06-02.
- ↑ Faylor, Chris (2010-06-09). Valve Delays Portal 2, Confirms E3 Surprise Is 'PORTAL-2-THEMED-FOR-GOD'S SAKE'. Shacknews. Retrieved on 2010-06-09.
- ↑ Francis, Tom (2010-06-15). Valve’s E3 surprise is... oh. Portal 2 on PS3. PC Gamer. Retrieved on 2011-06-26.
- ↑ Bramwell, Tom (2010-03-05). Portal 2 due out this Christmas. Eurogamer. Retrieved on 2010-03-05.
- ↑ Gay, Gregory (2010-08-18). Portal 2 Teleports to Shelves Next February. Escapist. Retrieved on 2011-04-21.
- ↑ de Matos, Xav (2010-11-18). Portal 2 Delayed to 'The Week of April 18'. Shacknews. Retrieved on 2010-11-18.
- ↑ Newell: Portal 2 'pretty much' ready for release. Computer and Video Games (2011-02-19). Retrieved on 2011-02-20.
- ↑ Faylor, Chris (2010-03-08). Steam Coming to Mac in April, Portal 2 This Fall. Shacknews. Retrieved on 2010-03-08.
- ↑ Graff, Kris (2010-12-22). EA, Valve Confirm Distribution Agreement For Portal 2. Gamasutra. Retrieved on 2010-12-22.
- ↑ Brown, Nathan (2011-04-20). Potato Sack Developers Helped Design Portal 2 ARG. Edge. Retrieved on 2011-04-20.
- ↑ Phillips, Tom (2011-04-13). Portal 2 to get early release on Steam?. The Metro. Retrieved on 2011-04-13.
- ↑ Greyson, Nathan (2011-04-13). Portal 2 to release early? Potato sack ARG signs point to "yes". VG247. Retrieved on 2011-04-13.
- ↑ Senior, Tom (2011-04-13). Portal 2 levels appear in potato sack games, clues suggest Portal 2 could be released early. PC Gamer. Retrieved on 2011-04-13.
- ↑ Kohler, Chris (2011-04-13). Valve May Release Portal 2 On Friday, Not Tuesday. Wired. Retrieved on 2011-04-13.
- ↑ Davidson, Pete (2011-04-15). Play indie games, help Portal 2 release early. GamePro. Archived from the original on 2011-12-01. Retrieved on 2011-04-15.
- ↑ Schreier, Jason (2011-04-15). Play Steam Games, Launch Portal 2 Early. Wired. Retrieved on 2011-04-15.
- ↑ Hillier, Brenna (2011-04-18). No more potatoes: Portal 2 available right now on Steam. VG247. Retrieved on 2011-04-18.
- ↑ 102.0 102.1 Hillier, Brenna (2011-03-17). Valve's in-house Portal 2 ad the result of "copycat" agency treatments (Update). VG247. Retrieved on 2011-03-17.
- ↑ Molina, Brett (2011-03-22). Trailer Park: 'Portal 2'. USA Today. Retrieved on 2011-03-22.
- ↑ Davidson, Pete (2011-04-19). Portal 2 goodies now on sale. [amePro. Archived from the original on 2011-12-01. Retrieved on 2011-04-19.
- ↑ 105.0 105.1 Schiesel, Seth (2011-05-10). Physics, With Wormholes by You. New York Times.
- ↑ 106.0 106.1 106.2 106.3 106.4 Salen, Katie (2012-11-13). How Portal 2 Developers Became The Best 6th Grade Physics Teachers Ever. Fast Company. Retrieved on 2012-11-14.
- ↑ Alexander, Leigh (2012-06-20). Valve helps educators Teach With Portals. Gamasutra. Retrieved on 2012-06-20.
- ↑ Narcisse, Evan (2012-06-20). Valve Gives Away Portal 2 for Free to Teachers with ‘Steam for Schools’. Kotaku. Retrieved on 2012-06-20.
- ↑ 2010 Winners. fGame Critics Awards (2010-07-06). Retrieved on 2010-07-06.
- ↑ Snider, Mike (2010-06-29). E3 2010: Game Critics Awards nominees announced. USA Today. Retrieved on 2010-06-30.
- ↑ E3 2010: Best of E3 Awards. IGN (2010-06-17). Retrieved on 2010-06-30.
- ↑ GameSpy's Best of E3 2010 Awards. Gamespy (2010-06-25). Retrieved on 2010-06-30.
- ↑ Anderson, Joe (2010-12-10). Spike VGA 2010 winners – Red Dead Redemption scoops GOTY. VG247. Retrieved on 2011-05-27.
- ↑ Cowen, Danny (2011-04-20). Critical Reception: Valve's Portal 2. Gamasutra. Retrieved on 2011-04-20.
- ↑ Ivan, Tom (2012-01-13). Narrowly beats The Elder Scrolls V: Skyrim on Xbox 360 to take the top review spot. Computer and Video Games. Retrieved on 2012-01-13.
- ↑ 116.0 116.1 116.2 Nelson, Mike. Portal 2 Review. 1UP.com. Retrieved on 2011-04-21.
- ↑ 117.0 117.1 117.2 117.3 Welsh, Oli (2011-04-19). Portal 2. Eurogamer. Retrieved on 2011-04-19.
- ↑ 118.0 118.1 Molina, Brett. Review: 'Portal 2' aces the sequel test. USA Today.
- ↑ 119.0 119.1 119.2 Sapieha, Chad (2011-05-01). Portal 2 is for smarty-pants only. Globe and Mail. Retrieved on 2011-05-01.
- ↑ 120.0 120.1 120.2 Webb, Morgan (2011-04-19). Portal 2 Review – Xbox 360. G4 TV. Retrieved on 2011-04-19.
- ↑ Cowen, Nick (2011-04-19). Portal 2 – Review. The Guardian. Retrieved on 2011-04-19.
- ↑ 122.0 122.1 Freeman, Will (2011-04-23). Portal 2 – review. The Observer. Retrieved on 2011-04-23.
- ↑ Kuo, Ryan (2011-04-19). Portal 2 Is A Hole In One. Wall Street Journal. Retrieved on 2011-04-19.
- ↑ Mastrapa, Gus (2011-04-25). Portal 2. A.V. Club. Retrieved on 2011-04-25.
- ↑ 125.0 125.1 125.2 125.3 125.4 Onyett, Charles (2011-04-19). Portal 2 Review. IGN. Retrieved on 2011-04-19.
- ↑ Martin, Garrett (2011-04-25). ‘Portal 2’ sure to gel with fans. Boston Herald. Retrieved on 2011-05-01.
- ↑ Frum, Larry (2011-04-19). 'Portal 2' is a dark, humorous joy (and that's no lie). CNN. Retrieved on 2011-04-19.
- ↑ 128.0 128.1 Narcisse, Evan (2011-04-19). Portal 2 Review: Our First Perfect 10. Time. Retrieved on 2011-04-19.
- ↑ 129.0 129.1 129.2 Stapleton, Dan (2011-04-19). Portal 2 review. PC Gamer. Retrieved on 2011-04-26.
- ↑ 130.0 130.1 Portal 2 Review. Edge (2011-04-19). Retrieved on 2011-04-30.
- ↑ 131.0 131.1 Young, John (2011-04-20). 'Portal 2' videogame review: Physics is phunny. Entertainment Weekly. Retrieved on 2011-04-20.
- ↑ 132.0 132.1 132.2 Biessener, Adam (2011-04-18). Portal 2. Game Informer. Retrieved on 2011-04-19.
- ↑ 133.0 133.1 Bright, Peter (2011-05-02). Thinking on rails: why Portal 2 isn't as good as the original. Ars Technica. Retrieved on 2011-05-02.
- ↑ 134.0 134.1 134.2 134.3 Watters, Chris (2011-04-19). Portal 2 Review. GameSpot. (archived)
- ↑ Gifford, Kevin (2011-05-11). Japan Review Check: Portal 2, Ghost Recon. 1UP.com. Retrieved on 2011-05-11.
- ↑ Hamilton, Kirk (2011-04-26). Portal 2 Review (Multi-Platform). Paste. Retrieved on 2011-05-05.
- ↑ 137.0 137.1 Kohler, Jeff (2011-04-21). Portal 2 Review. Wired. Retrieved on 2011-04-21.
- ↑ The Escapist : Building Sequels Badly. Escapistmagazine.com. Retrieved on 2013-04-22.
- ↑ Jenkins, David (2011-04-20). Fans protest Portal 2 on Metacritic. GamesIndustry.biz. Retrieved on 2011-04-20.
- ↑ metrowebukmetro (2011-04-20). Portal 2 hit by user review backlash on Metacritic. Metro. Retrieved on 2011-04-20.
- ↑ Tolito (2011-04-19). The People are Panning Portal2. Kotaku. Retrieved on 2011-04-19.
- ↑ Walker, John (2011-04-19). Let's Address Some Portal 2 Nonsense. Rock Paper Shotgun. Retrieved on 2011-04-19.
- ↑ Dutton, Fred (2011-04-19). Portal 2 Metacritic user score pounded. Eurogamer. Retrieved on 2011-04-19.
- ↑ Handrahan, Matthew (2011-10-21). Portal 2 voted GOTY at Golden Joysticks. GamesIndustry.biz. Retrieved on 2011-10-21.
- ↑ Portal 2 – The Top 10 Everything of 2011 – TIME. Time (2011-12-07). Retrieved on 9 December 2011.
- ↑ Gamasutra's Best Of 2011: Top 10 Games Of The Year. Gamasutra (2011-12-23). Retrieved on 2011-12-23.
- ↑ IGNs 2011 Game of the Year Video on IGN.com
- ↑ Eurogamer's Game of the Year 2011. Eurogamer (2011-12-31). Retrieved on 2011-12-31.
- ↑ Fahey, Mike (2012-01-02). Portal 2 Takes Kotaku’s 2011 Game of the Year Award for Science, You Monster. Kotaku. Retrieved on 2012-01-02.
- ↑ 'Portal 2,' 'Skyrim' top a thrilling year in games (2011-12-21). Retrieved on 2011-12-21. (archived)
- ↑ Lynch, Kevin (2011-12-23). Portal 2, The Witcher 2 and Uncharted 3: Drake's Deception... the top 10 video games of 2011. Daily Mirror. Retrieved on 2011-12-23.
- ↑ Orland, Kyle (2011-11-16). Portal 2 Leads Spike TV VGA Nominees With 12 Nods. Gamasutra. Retrieved on 2011-11-16.
- ↑ Cork, Jeff (2011-12-11). Skyrim, Portal 2, Arkham City Won Big At VGAs. Game Informer. Retrieved on 2011-12-11.
- ↑ Portal 2, Skyrim, Bastion lead finalists for 12th annual Game Developers Choice Awards. Gamasutra (2012-01-05). Retrieved on 2012-01-05.
- ↑ Skyrim wins Game of the Year at GDC Awards. Gamasutra (2012-03-08). Retrieved on 2012-03-08.
- ↑ 15th Annual Interactive Achievement Awards Finalists (PDF). Academy of Interactive Arts & Sciences (2012-01-13). Retrieved on 2012-01-13.
- ↑ Bertz, Matt (2012-02-09). Skyrim Dominates The 15th Annual Interactive Achievement Awards. Game Informer. Retrieved on 2012-02-09.
- ↑ Molina, Brett (2012-02-16). 'Batman,' 'L.A. Noire' lead BAFTA game award nods. USA Today. Retrieved on 2012-02-21.
- ↑ Portal 2 wins best game at the Bafta Video Game Awards. BBC (2012-03-16). Retrieved on 2012-03-16.
- ↑ Curtis, Tom (2012-03-14). Battlefield 3, Portal 2, more win big at 10th annual G.A.N.G. Awards. Gamasutra. Retrieved on 2012-03-14.
- ↑ Schiesel, Seth (2012-02-03). Skyrim Wins Video Game Critics Award. New York Times. Retrieved on 2012-02-07.
- ↑ Nunneley, Stephany (2012-10-26). 2012 Golden Joystick Awards – Skyrim wins Ultimate Game of the Year. VG247. Retrieved on 2012-10-26.
- ↑ Cowen, Danny (2011-04-22). Saling The World: Portal 2 Leads Cross-Platform Charts Worldwide. Gamasutra. Retrieved on 2011-06-27.
- ↑ Cowen, Danny (2011-04-29). Saling The World: Mortal Kombat Overtakes Portal 2 Stateside. Gamasutra. Retrieved on 2011-04-29.
- ↑ Dutton, Fred (2011-05-12). NPD: Mortal Kombat beats Portal 2 in US. Eurogamer. Retrieved on 2011-06-27.
- ↑ 166.0 166.1 Klepek, Patrick (2011-06-22). Portal 2 Has Sold More Than 3 Million Copies. Giant Bomb. Retrieved on 2011-06-022.
- ↑ Graft, Kris (2001-06-13). NPD: May U.S. Retail Game Industry Sales Lowest Since Oct. '06. Retrieved on 2011-06-27.
- ↑ Rose, Mike (2011-04-26). Portal 2 Scores Valve First Ever Top Spot In UK Sales Charts. Gamasutra. Retrieved on 2011-04-26.
- ↑ Rose, Mike (2011-05-03). Portal 2 Holds On To Top Spot For Second Week In UK Sales Charts. Gamasutra. Retrieved on 2011-05-03.
- ↑ Matthews, Matt (2011-06-21). Analysis: Did The PSN Outage Hurt U.S. PS3 Hardware Sales?. Gamasutra. Retrieved on 2011-06-27.
- ↑ Graft, Kris (2001-04-26). Developers Say PSN Outage Affecting Sales, But Remain Hopeful. Gamasutra. Retrieved on 2011-06-27.
- ↑ Anderson, Joe (2011-04-26). Has PSN outage affected Portal 2 PS3 sales?. ShopToNews. Retrieved on 2011-06-27. (archived)
- ↑ Orland, Kyle (2011-06-22). Newell: Portal 2 Has Sold 3 Million Copies. Gamasutra. Retrieved on 2011-06-22.
- ↑ Dutton, Fred (2011-07-26). Crysis 2 racks up three million sales. Eurogamer. Retrieved on 2011-07-26.
- ↑ Nutt, Christian (2011-08-29). The Valve Way: Gabe Newell And Erik Johnson Speak. Gamasutra. Retrieved on 2011-08-30.
- ↑ Caoili, Eric (2012-05-08). Portal 2 has sold over 4M copies. Gamasutra. Retrieved on 2012-05-08.
- ↑ http://steamcommunity.com/stats/Portal2/achievements/
- ↑ http://www.xbox360achievements.org/game/portal-2/achievements/
- ↑ http://www.ps3trophies.org/game/portal-2/trophies/
- Official Portal 2 website
- Game Informer's Portal 2 March 2010 Hub
- Portal 2 section of the Steam forums
- Teach With Portals