In the playable Half-Life 2 leak, the OICW is essentially an AR2 Pulse Rifle with a scope instead of the energy ball thrower. Its recoil makes it very difficult to control past five shots in a row. However, this can somewhat be reduced by crouching.
It uses medium rounds, which are also used by the AK-47, the MP5K, and the MP7.
In real life, the OICW features a grenade launcher. While not working in the leak (it is in the source code, but is disabled), it was shown working in promotional videos. It appears that its grenade function was moved to the SMG1 by the time the files were leaked, as getting close to the SMG grenades in the WC mappack map "zoo_item.vmf" causes the message "AR2 Grenades" to appear on the screen.
Screenshots featuring the OICW in Half-Life 2: Raising the Bar show an early model with a texture that made it look very damaged and used. This texture is still in the playable leak files, as seen below.
An unused texture file for the Conscript model features a bayonet at the end of a barrel, but it is unknown if that barrel was to be that of the OICW.
Interestingly, the scope on the OICW when unzoomed is broken in-game (it shows a solid light green instead of the scope texture), while it works properly when viewed with the leak model viewer.
In the final version of Half-Life 2, the Rebel's reload animation for the AR2 Pulse Rifle is the same as the OICW's in the playable leak.
In the Half-Life 2 files, several texture files for HUD weapon icons can be found, most of which still containing the icons for almost all of the cut weapons. The OICW is among them. It is also present in the font "HalfLife2.ttf", used for all the HUD glyphs.
The retail MP7's grenade model is still named "ar2_grenade.mdl".