Jak and Daxter comes to mind, as well as the first 2 Fallouts and hell I'll even throw in Tactics as well or the .Hack games, yes all 7 of them. But the ONE game I will play until I can no longer hold a controller (which by then i should be able to get robot hands
) would be Suikoden 3, yes I love the two before it but 3 was the first in the series and will always reign supreme for me, if I could only ever play one game for the rest of my life I think that would be it.