Satangel: yeah this is an old topic. I had to check all pages to make sure I hadn't already voted (turns out I haven't yet)
but wow this is a difficult question, I'm not sure I can answer that.
I've had best games in different times of my life. When I was a kid, I used to be completely into Zelda: Link's Awakening, on the original GB. I'd play this game for hours and beat it again and again.
Same can be said for Metal Gear Solid 1, then 2, and then 3...
But overall, I think my all-time favourite game is probably The Legend of Zelda: The Wind Waker.
A unique colorful game, with an excellent storyline (compared to the usual zelda game), awesome experience overall. Yeah.