Alien swarm is another great co-op game made by the King Of Co-Op lately Valve.
First off this game looks great even though its done on the Source engine, which doesn't really have the best looking games around. The gameplay is soild after my hours of playing this game, I hadn't found any issues with the gameplay and neither did any of my fellow space people. Sound is alright, the guns sound great but as I was playing I didn't pick up on any of the alien sounds, not to say they ain't there. Just couldn't hear them over the constant gun fire. The only bad thing about this game is that the amount of levels you have isn't nearly enough, because the eneimes don't random they always come the same way etc. But the most important thing is this game is free and it is well worth your time.
