Counter strike global offensive. I've played every FPS under the sun, but nothing has kept me entertained for as long as csgo has.
Some pro's:
Only 15$ (Canadian)
5v5 competitive matchmaking
Casual matchmaking
Loads of community servers with various different gamemodes
Relatively good anti-cheat (VAC)
Never heard of that, but then again, I need to look into that more.
Thanks