About as good as it gets for $6.
Bit.Trip: Beat is an unusual game for Nintendo's downloadable service, Wiiware. I like to think of it as the result of Guitar Hero and Ikaruga somehow managing to simultaneously impregnate Pong after a long night of romance and ecstasy. The reasoning behind the first is that, simply put, the beat of the music is very much an essential part of the experience. It's comparable to Ikaruga in the sense that the 2D gameplay can get incredibly frantic, almost to the point where you don't know what you're looking at on screen anymore. And lastly, the similarities to Pong are obvious and undeniable, using a paddle to deflect the "beat" back from wince it came. These elements of gameplay mesh rather beautifully, and the final product is one that's both unique and engaging.
With three levels in the package, the argument that its a little light on content is a valid one. Though, at $2 a song each running anywhere from 10-15 minutes (and with high scores and local leaderboads), there is plenty of variety, replayability, and challenge here to make it worth your time and money.