Left 4 Dead 2.
The community really keeps me playing. You can talk as much smack as you want and nobody condemns you for it. The teamwork aspect is amazing in competitive games, especially in tournaments. You really get a feel for the game and what you're supposed to do as each special infected and with each weapon. The tactile strength, reflexes, and aim accuracy I have built from playing this game is unimaginable, I feel as if I am greater at any other game I play, even ones I've previously played but never really got better at. PromodHR is probably my favorite gameplay mod and it will continue to be for as long as I play.
