Have you tried Rocket - Robot on Wheels? It's not as good as some of the others, but it's definitely the same sort of game as Banjo, and I thought it was pretty fun (especially with an emulator where you can save anywhere - much less frustrating).
I haven't played Spacestation Silicon Valley, but it got pretty good reviews, and it also looks like an adventure-type game.
Chameleon Twist 2 is more of a straight 3D platformer (more like Super Mario than Mario64 is!) but it has some tongue-action moves (heh that makes it sound like Conker) that are kind of fun.
Hercules is kind of a bad Zelda clone. I enjoyed the first level with the Cyclops, but then it started to suck. Don't know if it gets any better.
Bomberman Zero and Megaman are also adventure games and got so-so reviews (haven't tried them).
But don't diss Diddy Kong! That is an extremely fun game. It has some adventuring (looking for keys, collecting balloons, finding secret doors) and it is an extremely well-done racing game. For bosses, instead of racing a extra-fast car you get to race a huge dragon, dinosaur, or giant octopus! And when you've won a lot of races, to up the difficulty, instead of making all your opponents faster, you have to race the courses collecting 8 coins *and* win the race. It forces you to take a more varied route and makes it much more interesting than just racing the same way only faster.