For multi it's gotta be BF3. For single player awesome story and proper stealthy gameplay it's gotta be Dishonoured. I've got 3 missions left of my first playthough on Dishonoured but I can see myself starting the second playthrough minutes after completing the first!
Going to replay Half-Life 2 + Episodes (Never finished 2) Counter-Strike Team Fortress 2 ( quite like this one on a good map and decent server ) When new gfx card arrives ill be purchasing some games (4830 doesn't quite cut it any more) Bad Company 2 (already have but unplayable) BF3
Red Orchestra Heroes of Stalingrad would be a good title if you have any interest at all in WW2 Best WW2 shooter ever made, even if TW did let this latest release down somewhat. There is an expansion on the horizon which will include American and Japenese troops. There is some great community made maps being released now which adds to the game greatly.
You might want to try 'Quake Live', it's basically Quake 3 Arena but free and browser based. The server browser interface is far superior to the basic Q3A one and the game itself works properly on newer systems while the old one seems to be pretty dodgy stability-wise.