Uha, tough one. I think it doesn't hold up today but for me it will have to be Conker's Bad Fur Day, just because of what it was at the time- after years and years of getting mocked by the Pro-Playstation crowd for the family friendly games on Nintendo64, Rare's swan song started with Conker cutting the N64 logo in two with a chainsaw and didn't stop for the rest of the game with splatter, feces humor and sexual innuendo- with more voice acting than 98% of other N64 games combined. Just what the doctor ordered at that time. Other mighty honorable mentions: Diddy Kong Racing (oh yes, it was better than Mariokart64), Goldeneye, Perfect Dark, Super Smash Bros and Mario Tennis.