Man, I don't know which one to vote for. BF2, HL², and CS:S have awesome physics and destructable environments. I have been waiting to play SWAT 4 for quite a while. And Splinter Cell: Chaos Theory has Multiplayer Co-Op which is so awesome (I saw some clips of it). I think I am going to go with CS:S even though I have never played regular CS. I'm serious I have never played CS.