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* Addictive co-op action gameplay from the makers of Counter-Strike and Half-Life
* Advanced artificial intelligence drives both friendly and unfriendly creatures to dynamically create intense single-player, co-op, and multiplayer experiences every time the game is played
* 20 maps and 10 new weapons over four sprawling campaigns
* Match making, stats, rankings, and awards system drive collaborative play
* Designer's Commentary mode allows gamers to go behind the scenes of the game
* Powered by Source and Steam