I was distraught at SMB at first, but now that I've put some time into it It's really starting to click. The Main game was made for the Wii-mote, there's no question. In some cases it's more challenging than the GC SMB and SMB2 control, but after a while, it becomes second nature and you'll find yourself rocking with it (no pun intended).
The mini games on first run through seem insurmountably difficult, but it's all just a quick learning curve. It's really a kind of a an all out exhibition of what the the Wii controls are all about.
Some of the highlights...
Fish Scoop...a mini game where you hold the wii-mote like a goldfish net and have to scoop fish out of a bucket. It really makes you have to use the remote in true 3-D space to get it right.
Monkey War (I think is the name)...it's first person shooter that from a contol standpoint puts Red Steel cpntrols to shame (don't get me wrong, it's not that deep, just proof that the mote/chuck combo CAN work well with FPS).
Monkey Race...if you don't have any racing games yet, this is a nice scratching of the surface of how steering feels with the wii-mote. Very natural...controls well.
Spear Fishing...very cool application of spear fishing with the wiimote. Spear the fish and pull them back to yourself.
Hammer Throw...simple hammer throw game where you hold the wiimote up and spin it in a circular motion to build up speed for a hammer throw. Simple but fun.
The not so good...
Monkey Target...As someone else pointed out in a different thread, if your a Monkey Target fan they totally raped it. One Field, no pickups, no wind, no control of your launch (all identical from a cannon you don't control). I still spent a lont time with it, but overall they really screwed the pooch on my favorite mini from the first two installments.
Frisbee Golf...this is good and bad. Very cool from the standpoint of actually having to simulate frisbee throwing motion, very sensitive to the strength of your toss, but the obstacles are infuriating. When you get stuck between two trees it's almost impossible to discern what the hell you have to do to get out in a reasonable amount of throws.
Overall, even though spear fishing is the exception, I think the big weakness with Wiimote motion so far is moving in and out quickly to perform tasks. It gets very difficult and frustrating. I also hate that about "zoom" in Red Steel. It's one of the wii-mote motions that doesn't feel natural and keeps you from being able to "relax" and play a game.
Mini-games in general...it always ends your game and takes you back to the menu after you play once. A little criticism, but HEY, if I like the mini-game, did the Dev's ever think someone MIGHT want to play it again without exiting out to the menu? just a nit-pick I guess...
Overall, if you are going to buy or rent Monkey Ball, I urge you to work through the learning curve. It's a very different experience than the first two games on the surface, but rewarding once your comfortable with the controls. Just my 2 cents. The criticisms so far are fair, but it's a great all around showcase for the Wii-mote...and there is fun to be had with it.