Easily Zelda: Ocarina of Time. My first game for the N64, and practically my first 3D game in general. I bought it not even knowing what Zelda was, but because I liked the sword and sheild cover. Bear in mind I was 8.
Imagine my surprise. Just try. Before that the best game I'd ever played was Doom.
GOTY Contestants this year: Dead Space 2, Dark Souls, Tales of Graces f. Everything else can suck it.