eh - I wouldn't call Banjo Kazooie my favorite platformer of all time (better than mario? Are you nuts?)....but I did really love it. The thing that sold the game was the absolutley incredible sense of style and humor. The game featured what is probably the best platformer overworld ever, and the best charachters/dialogue in a platformer ever. Add to that all kinds of little touches - from the creative save-game select screen, to the mole who teaches you new moves, to your character's house which doesn't really need to be there but is anyway. And then the gameplay, which is more character-driven and open-ended than Mario 64, is just top-notch. The game really throws all kinds of awesome, creative challenges at you.
The game gets a lot of flak these days for being too much the collect-a-thon, but really, it's not. Remember that, at the time, the game was ridiculously well received....and I think it deserved it. I think people tend to lump it in with DK64 and the like - forgetting, perhaps, that it really wasn't that bad. Requiring you to collect musical notes was definitely a bad idea, but, unlike DK64, collecting only became a pain towards the very end of the game.