* 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 new maps. 10 new weapons. 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.
Thought this was the cheapest around?