Not in any order, just my top 3 which share the top slot.
Far Cry
Doom 3
Return to Castle Wolfenstein (yeah i still play it online 2-3 times a week).
Their are a few close seconds as well including H/L 1&2 Unreal Tournament 2004 and Call of Duty.
Looking forward to fear as it looks great on paper, and the demo is good as far as demo's goes.