The Lowdown: Wii Music is that game Shigeru MIyamoto played at Nintendo's E3 press conference two years ago. The main mode is an up-to-four-player "band jam" mode that lets you play parts of a song with various instruments, improvising freely, while recording your "performance" as represented by your Miis. Then you can send the video to any other Wii Music user over WiiConnect 24. The game also features orchestra conducting, handbell playing, music quizzes, and a Balance Board mode that lets you play simulated drums.
The Hype: Wii Music is a game for people who don't want to play something like Guitar Hero or Dance Dance Revolution, that is really about rapidly matching colors/buttons roughly in time with the beat. Instead, it's about making music, something current rhythm games don't support well.
The Snark: Every demo of the game and its fact sheet information leave me with the impression that this game basically plays itself. You move the Wii Remote or Nunchuk and the game strives to make it sound good based on your motions. You can only really fail in band jam mode.
Press kit screens behind the cut.