Black Ops and Modern Warfare 2 COMBINED are already played less on the PC than just Counter-Strike 1.6, not even counting Source (check Steam statistics, Black Ops is a Steamworks game).
Yeah it's different if you count consoles. But relying on console tards to tell us whats a good multiplayer FPS is like asking a four year old what good cuisine is. He'll tell you pancakes and you'll want to slap him across the face.