So far the only game I've picked up that I've been even a little disappointed with is Super Monkey Ball: Banana Blitz. The 1 player is kind of fun (though extremely challenging by world 5), and there are a couple of fun multi-player games (darts probably being my favorite) but most of the games have really unpolished controls.
SSX Blur is probably my favorite. It took me a while to get the über tricks down, and slalom is still a bitch, but overall it's really fun. Even though I've played all the tracks now a zillion times, it's still fun. The nunchuck carving interface is brilliant.
I finally got around to beating The Legend of Zelda: The Twilight Princess. A really good addition to the Zelda family. The story seems very very japanese, but the game was a lot of fun and there were lots of fun, interesting, sometimes mind-bending puzzles.
Rayman Raving Rabbids was clearly developers experimenting with what the Wii can do, but they put enough polish on the controls and presentation that most of the gameplay is fun and the humor is delightfully twisted.
Excite Truck I have logged a shit-load of time on. I working on opening up the mirror tracks and completely the Super Challenges. Really awesome game, shame about the two-player mode sucking so much.
Wii Sports was brilliant as a pack-in, my bro and I play tennis all the time and when we get together with a bunch of people Bowling is always a favorite. I do wish you could have more than 4 players in bowling. The golf game is simple but fun, and I'm not so big on the baseball or boxing.
That's all the games I have so far. I'm thinking that once I acquire a source of income my next purchase will be Super Paper Mario.