Hmmm... to hard to narow it down, especialy since there are so many Genre.
Platform/Action:
NES: Super Mario Bros. 3... That game was one of the longest and really pushed the NES hardware to its limits. Besides, its hard to keep the Mastashoid down.
SNES: Yoshi's Island... That game finally put Yoshi to full blown stardom. It was the most enjoyable, and most beutifull games. Not to mention that its freally fun to swallow and poop out you enemies as eggs.
N64: Conker's Bad Fur Day... Who knew that a game Developed by Rare that first started as a normal , so cute game you could barf game into such an enjoyable, major motion picture spoofing, foul mouth, dung rolling, discusting, so bloody game you could barf game.
GCN: Hmm... at the Moment... Super Mario Sunshine... its a true to the heart Mario Game, 'nuff said.
RPG
SNES: Super Mario RPG: Legend of the Seven Stars... it was a well though through game that perfectly put Mario and the Mashroom Kingdom in the the RPG world.
GB/GBA: Pokémon... 'nuff said
Adventure:
SNES: The Legend of Zelda: A Link to the Past... the only Zelda game for the SNES. It Rocked!
N64: The Legend of Zelda: Ocarina of Time... Can there possibly be a better Adventure game!? This game was so awsome, all adventure games that followed were compeared to it and still don't come close.
GCN It a Tied... The Legend of Zelda: The Wind Waker and Metroid Prime... StarFox Adventures was good, but not good enough to go on my favorites list. Wind Waker was awsome. Not only did it have a good storyline, but I think the new Cel-shading technique fit in perfectly with the series. That how a Zelda game should have always lookd like. And Metroid Prime!!! The Graphics were outstanding, The Storyline was compeling, The controls were tight and well layed out, and the score pulled in.
Racing:
The F-Zero and Mario Kart Series. F-Zero gave birth to the whole futuristic, techno racing genre and Mario Kart gave birth to true multiplayer fun.