Wii Music is hard to judge as a video game. Comparing it to other rhythm action games would be unfair because it attempts to be an exercise in fun and innovation. It achieves the fun factor in some respects; custom jamming is enjoyable and surprisingly deep, especially with two or more players. It is well presented and seeing your Miis make up a band is funny.
However, Wii Music is let down, like so many other Wii games, by a Wiimote that doesn't quite live up to its original billing and because it has very little meat on the bones in terms of gameplay. Wii Music is fun and has bags of potential, but much like Wii Sports it feels more like a tech demo than an actual game; only this time you'll be paying £30 for the pleasure.