Dude, I'm getting a Wii!

If you're going to get the couple of 2d platformers you mentioned in the op, I'd say its probably a good idea to get NSMBwii too. It's not -as- good in single player as it is multiplayer, but its still a decent 2d mario game. also, Wario world: the shake dimension , or whatever you crazy americans are calling it (Wario land: shake it? I think)

Anything else? Mostly into RPGs

The wii is a bit bare in this area, but Final fantasy: the after years (wiiware- download game) is a decent game, -expect to pay a lot for all the extra download chapters though.
Fire emblem: Radiant dawn is a good turn based strategy game-,much better than the pomegranate ds fire emblem game, though the plot is quite ... odd. Should probably play the gamecube game, fire emblem :path of radiance first if you haven't (gamecube game), since its a sequel storyline wise.
Maybe monster hunter tri, though I hate the game, it seems to be a you love it or you hate it thing.
Rune factory frontier is decent cross between a standard rpg and harvest moon, though if you don't like harvest moon games , I wouldn't recommend it.

Aren't Galaxy games just spiritual sequels to 64 and Sunshine? How can you call them "unlike any game [you]'ve played" when they're essentially the same "do 7 missions on each level like getting red coins"

Nah, galaxy 1/2 (2 being the better of them imo, it has yoshi! and not in the cameo way sunshine had him) is much better than the mess that is 64 (face it people , it aged terribly), galaxy 1 and 2 are much more like a 2d mario game than either of the previous entries. By that I mean, apart from the purple coin stages, the objectives are almost all "get to the end of the stage for a star!". I think not at least renting one of the two to give it a shot isn't doing them justice, but in the end its up to you.

If you like fighting games, I'd suggest Budokai Tenkaichi 3. It's Dragon Ball and I don't know if you like that much, but the game itself is fun as hell.

Budokai tenkaichi 2 is better. Don't get either of them if you don't like dragonball though.

I hear Other M is terrible.

You hear wrong. Its not close to as good as the prime games, but its certainly not terrible, though it is below normal nintendo standard (i.e., maybe 80%ish if we were talking review scores)..

Also, seconding Muramasa. It's an excellent 2D sidescroller with RPG elements, just like Odin Sphere. It can be pretty difficulty particularly during bosses.

Thirding muramasa, though don't go in expecting anything difficult at all outside of boss fights, the game is hilariously easy and every enemy thats not a boss can be dealt with in exactly the same way.

I disliked zack and wiki, i really tried to like it, and I enjoy puzzle games, but some of the levels are just pineappleing stupid, and being able to die in a puzzle game = lol. It's more of a trial and error game than a puzzle game