Call of Duty 4 "Modern Warfare", that was it for me, I ended my computer video game career with that game. Haven't played anything else since!
That is a classic, I'd say. Yeah, loved that game, too. The sniper mission in the campaign was absolutely epic -- that part where the two snipers dig in near the Ferry's Wheel to wait for the hostiles to come in from the far edge of the field.
I seem to remember the multiplayer version had a mode where you started off unarmed -- which I thought was pretty cool.