In the version I played, there were only two levels open. Though I couldn't hear the music, aside from faint sounds of the bass, the game was still a lot of fun. Played with the Wii Remote being held like an NES controller, your paddle is controlled by tilting the Wii Remote forward and backward. The goal is to block the various balls from getting past your paddle as you keep up with the beat of the music. It is very simple, but it's very addictive, much like the recent WiiWare release, Maboshi's Arcade.
As you play, you develop a multiplier that goes up with every successive ball you block, thus increasing your score. If you do poorly, you are sent to the black-and-white purgatory where you must fight your way out by not letting balls by you. It is an accessible and relaxing game yet it can be very intense.
While Bit.Trip Beat allows for up to four simultaneous players, I was only able to play with two. The co-op mode does offer some fun gameplay possibilities as it requires a lot of communication between the players because, as you gain more players, the paddles gets smaller.
The co-op mode was my biggest draw to the game and will likely be what wins me over when Bit.Trip Beat hits WiiWare for somewhere around 500 or 600 Wii Points in the next month or two.
