All Half-life games. If you want to relive the original Half-life, you can do it by playing the Black Mesa version in the half life 2 engine. Portal 1 and 2 if you want something puzzle heavy but still entertaining story. I still like playing the original Halo too. Serious Sam and Left4Dead is you're craving coop action. Deus Ex, System Shock 2 and of course Mass Effect if you want RPG with your FPS. Fear, Doom 3 and Deadspace are good for some sacredness... BOO! The older Call of Duties (1 through 5) are fun of you don't mind story heavy, linear experiences, Battlefield and Counterstrike for good multi-player. The BioShock games are worth trying. The Last Of Us if you have a PS3/4 if you really want some serious story. The original Far Cry of you want to mix some stealth in your FPS.