I've only played 6 games for the Wii (I'm not including demos.), And I'm going to through brawl out the window cause that would be to expected, so that only makes 5. Out of those I would have to say...
1. Sonic and the Secret Rings
2. Link's Crossbow Training
3. Wii Sports
Sonic and the Secret Rings was great. The story was strange, but cool and original. The game play was fun and original with high quality motion controls not only for a near-launch title, but any Wii game. All that, and Erazor Djinn was an awesome villain. I mean, he's a Genie and he has a sword that like a straight razor! Heh, maybe that's were he got the name.
Despite being a freebie for an accessory, Link's Crossbow Training was really quite good. A Legend of Zelda game focusing on Bow and Arrow combat rather than swordplay ( Along with various other changes.) seemed odd at first but ended up working out very well. Its on the short side, I beat it in one day, but I keep coming back for more after owning it for more than two weeks. Also, one level was heavily based on my favorite Zelda game, Majora's Mask. In all, a fun game with high quality graphics and high replay value.
I've owned a Wii since last Christmas and I still play Wii Sports! Why? It's fun, plain and simple.
The game I didn't put on the list are Super Smash Bros. Brawl, Wii Play, and Spider-Man 3. Brawl is great, but like I said putting on the list would be to expected. Wii Play is fun, but... eh. The only reason I got Spider-Man 3 is because I found it for $10, and it's fun, but the motion controls just feel tacked on, like most license game on the Wii.
After playing more game's, I'm sure I'd be able to make a better list. For now though, This feels pretty right to me.