Only played half-life and it was good.
Also played COD for the DS, and it was pretty good as well, but it IS overmilked.
1. Call of duty Franchise.
while sometimes call of duty offers heart pumping and water cooler moments it just provides frustration and cheap deaths
2.Team Fortress 2
i find this game to be useless and boring. theres no unlockables levels, or anything, it's just shoot to kill. atleast for all the games i played on the 360
3. Half Life franchise.
while you get emerged in this games interesting take into the future, it just gets a little boring after a while