I want to get Monkey Ball just because I heard it has music from Hideki Naganuma (he did a lot of music for both Jet Set Radio games and Ollie King).
Here's my Wii line-up and my thoughts. Despite having had the system since launch, I really haven't spent much time with it.
-Swing Golf Pangya: Believe it or not, this is what interested me the most out of the launch line-up, and I have barely touched it. It looked incredibly bad on my TV, but that was before I got component cables. I need to go back and give it another chance.
-Wii Play: Fun with friends and my wife in short bursts. I have no desire to play this alone, and it got old in multiplayer pretty quick.
-Hajimete No Wii: Bought this because it came with a Wiimote for only 1000 yen more. It's okay for that price, I guess, and also got old after a few plays. I thought it was kind of funny that people were getting hyped up for the English version (although it should be expected on GAF, I guess) since there's really so little to do in this title.
-Zelda TP: Bought it at launch. Played for...two minutes? Sold it. Bought it back just recently real cheap.
-Excite Truck: Pretty fun in short bursts. Haven't completed it, but it's fun to play every now and then, and is great in two player. Visually it's not much, but it gets the job done, and you can thankfully use your own music (MP3s off an SD Card) to replace the awful, awful in-game buttrock.
-Odoru Made In Wario: Great game, but it doesn't have much replay value in my opinion. I didn't find much of a drive to go back and replay the various mini games like I did with the original Made In Wario on the GBA, but then I haven't been a huge fan of any of these games save for the original.
-Biohazard 4: A port of the GC version, with the bonus additions from the PS2 version, making excellent use of the Wiimote. I loved RE4 on the previous consoles, and this is the best version of the game by far. It plays fantastically (almost too easy at times, though), and is how more Wii-specific control games should be made. Now if only an ORIGINAL game would come out that's as good as this is...
-Mobile Suit Gundam: Just got this recently, and have only played a little, but it plays surprisingly well. Almost as well as Biohazard 4 does! It's basically a first-person shooter with Gundams...using the Wiimote and nunchuck, you move and shoot, dash, fly, and use your beam saber (by slashing with the Wiimote). It's a nicely done game that's like the Capcom-developed Gundam games in a first-person view.
-Guilty Gear XX Accent Core: Excellent port to the Wii. Yes, it uses the Wiimote and Nunchuck for simplified dumb waggle game play, BUT you don't have to bother. The game also uses the classic controller, Game Cube controller, and the Wii arcade joystick (pretty much made for this game) as well, for normal game play. This version is better than the PS2 port. It fixes the major game-freezing glitches and has better sound quality.
I would say the most time I've spent with the Wii has been using its internet functions and playing a ton of Super Mario Bros. and Punch-Out!!.