Unless you go out and buy a game with all the little plastic copies of instruments, this is probably as close you can get to real music with the Wii.
Like Wii Sports, this is an open-ended game - you have four main options (mini games, playing music, training, and watching videos of your performance), but as you progress you unlock extra tunes, lessons, stages and the like.
As a solo effort it's not going to blow you away with raw power, but it looks good and as a multiplayer experience can be just as much fun as Wii Sports.
Rather than it's apparent simplicity (which is rather unfair; unlike Guitar Hero, with this game you can make music in a fashion - rather than just copy the rhythm and notes of a piece exactly), it's the choice of songs that let this down. Not willing to license well known or modern music, we're left with a load of traditional American tunes and songs from old Nintendo games.
Given the control method, it's hard to see how they could have made this any more realistic. The motions you make are close enough to playing a real instrument, and they've decided to make this game all about timing - as there's no way of actually choosing the note you play.
All this adds up to a game that's very easy to play; in fact out of all the Wii games this is probably the one you can most easily show someone how to play in a few seconds - and that doesn't necessarily mean it's shallow and has no long-term gameplay.
It's fair to say they've aimed it at young children, but some parts of the game are still a challenge - the Pitch Perfect minigame serves a useful purpose if you are a musician and want to improve playing by ear.
Personally I think this is every bit as good as Guitar Hero, and other similar games. Perhaps it doesn't quite justify its price tag, but there's a lot more to this than shoddy party games such as Mario Party, Big Beach Sports, etc.