Here's a quick runthrough of some of the Wii games I have played so far and whether they are worth buying or not. Some of them I only tested for a few minutes, some of them I have and have played a lot. Please comment on what you want a longer review of.
Kororinpa: Marble Mania - Good with some frustrating bits
It's hard to give a score to Kororinpa because on the one hand it's amazingly cute with a nostalgic childhood atmosphere, but on the other hand it gets very hard very fast and becomes as frustrating as, say,
Elasto Mania. Its relatively low number of levels (45) has been criticized which I can only half agree with because while it is a low number, you just have to know every corner of those levels to be able to get times fast enough to unlock the many secrets (15 secret levels and 5 super-secret levels) of the game. I just wouldn't have included the "extra" 45 levels which are just horizontal mirrors of the original levels, which does not add that much to replay value. Also, multiplayer is just a split-screen race on the same levels. I personally would've enjoyed something like co-op levels or similar.
Super Monkey Ball: Banana Blitz - Great
I first thought Kororinpa was cuter and better but that was before I played Monkey Ball. Now I think of the two games as things entirely different from each other despite the similarities. It's not short (in the single player mode I'm now in around world 5 of 8, each with 8 levels plus bonus levels and the boss), the difficulty curve is done well, and there are 50 entirely different party games (only played three of them so far, and they were not just thrown together but genuinely made). The music is another fine point of the game, having some 80's video game music feel.
Mercury Meltdown Revolution - Good
Not as fast-paced as Monkey Ball and not as frustrating as Kororinpa, Mercury Meltdown Revolution is a really odd puzzle-ish game where you roll around a blob of mercury in various levels (I think over 150, but at least 100) of various themed laboratories. It's good because it's mercury and you can have bits of mercury fall off the level while it doesn't equal losing, and you can finish a level even if your time runs out, so it's not a very strict system, which helps in practicing (and figuring out) levels so next time you get it done on time. Its style is a bit old school and because of this the graphics don't look very great sometime, but overall it's a good game, more reminiscent of early 90's PC puzzlers than console action games.
Big Brain Academy: Wii Degree - Good and bad
I don't know how many types of games you have in the DS version but the Wii version definitely seems a bit short. Even though there's three difficulties to each game, there's only fifteen games, and each of them lasts one minute. When you play, it's a good game, but it just seems a bit short.
Red Steel - Bad?
The design of the menu when I launched it up was good. The style of the game itself seemed okay. But then the game started and something went wrong. The controls seemed awful. You turn left and right by pointing the Wii Remote to the left or right side of the screen. This emulates R2-D2's head movement much better than a human's, which is a problem if five yakuza are shooting at you at the same time. Because of this, I died in the second minute of the first level, how lame is that? I stopped playing after 15 minutes.
Sonic and the Secret Rings - Awful!
I loved the Sonic the Hedgehog games in their old day, I recently replayed them on the MegaDrive. And in the retro nostalgia frenzy that characterizes the buzz around the Wii, I thought that the Sonic Team would do something of that sort. But nooo. The result is basically a clunky, frustrating race game. First of all, they put Sonic into an Arabian setting a'la Prince of Persia (why, instead of it's well-estabilished original design which I miss dearly by the way?), and then gave it J-Rock music as background. Huh? Even worse, there is one J-Rock number in the whole game, and that plays over and over. You always hear the first ten seconds when the game starts, then you hear the same middle five seconds when you finish a level. It's even more frustrating because the lyrics are Engrish garble and I don't understand a word of it.
Because of the slow and unnecessary menu system, it took me almost half an hour to get through the tutorials. And then the big surprise came: most of the levels are the same level. There are a couple of levels and then you have 'missions' in them, meaning you run through the same level about 16 times to move forward in the game. And you have levels like "Don't break the jar!" where you run like hell for two minutes and then you accidentally bump into a jar in a tight curve, it breaks and the game goes "Sorry you failed" and you have to start again. I was very persistent because I couldn't believe this game is so bad, but it is. I'm sad because I missed Sonic and I would've liked a good Sonic game.
In any case, avoid this game at all costs.