I'll just go with current-gen to make things easier, and because I missed some gems last gem but I think I can say I'm more or less up to speed this gen:
-Bioshock
-Modern Warfare
-Oblivion
-Batman: Arkham Asylum
-Super Mario Galaxy (seriously, it's really fun when you're not trying to rush through it, and it's challenging when you go for all 120 stars)
-Endless Ocean
Yes, I'm tacking on one at the end that many people might not agree with, but I really liked that game a lot, and it was (basically) single-player only, and while the story wasn't the best, the game itself was a lot of fun.