Great multiplayer, with the game being let down by controls.
The control in the game is obviously unique to the Wii contoller. It involves you tilting the remote in the direction you want your monkey to roll to and pressing A to jump. It has been well thoughtout except for a minor issue - when things are getting tense and nearing towards the three second countdown or when there is a thin ledge you need to go across, the controls let you down as they aren't tight enough and you'll find yourself blaming the controls more than your gaming skill (or lack thereof).
In the single player mode you have to work your way round a bunch of different themed courses collecting bananas and avoiding obsticles. Although there are no enemies as such there are things that will attempt to shove you off the course and lose your life.
There are a vast number of multiplayer mini-games (around about 50) in Super Monkey Ball and most of them are up to good standard and even if you don't like some, you've still got a load of other ones to choose from. Some mini-games are stuff like balancing your monkey while it walks across a tightrope or a slightly Mario Kart style racer. Other games include (but are not limited to) Simon Says, Monkey Battle and bowling.
Super Monkey Ball: Banana Blitz is a good game for the Wii and it really is a friendly game to use which makes you feel all warm and fuzzy inside when you use it. A Wii must have.