[Karmapolice]

OpenArena - a free open-sourceQuake 3 clone

but before that i played Army of Two. The coop part is great but the game itself is way too short. I just bought it last Saturday, played it for more or less an hour everyday and now I'm on the last mission of the game. The online feature is lacking. I wish you could join somebody's single player game and vice versa just like in Crackdown.