The BIT.TRIP BEAT Soundtrack is, simply enough, the soundtrack to BIT.TRIP BEAT. If you want to sample it prior to purchase, it can be listened to (with the exception of the Steam-exclusive track) at the developer's soundcloud page: http://gaijingames.bandcamp.com/album/bit-trip-beat-original-soundtrack
It's largely an ambient chiptune soundtrack, as the music lacks any of the noises which are made from hitting the beats. This is unfortunate, as for many of the sounds, the "melody" is from the player's actions. Ideally, I would have preferred a version of the soundtrack which included the "perfect" run of a level, including the sounds from each bit being hit. That being said, the background is pleasant in its own right, so for a fan of the game, this soundtrack is worth looking into.
Note that the soundtrack should be thought of only as 6 tracks, as tracks 6-10 are short, containing the audio in between levels or when the player loses, etc.