Oh man. everytime I see a question like this I get stuck for a while trying to single out one game that's better than the rest, but it just can't be done.
Zelda OOT is a really good game, I'll just go with that.
For me (both my consoles have been broken for a while, so I don't play too many games all around anymore, except for stuff on sites such as AG) I'd have to say World of Warcraft.
My brother would probably say an oldschool game such as Zelda, Ocarina of Time. Something on the Nintendo 64. He was cool. =)
The Secret of Monkey Island is esily up there. Brilliant characters and quotes that are famous (for me anyway). Also one of the best storylines I have ever seen.