Ultimate Band is a music game in which players hit notes in time with a scrolling display, using only the Wiimote and Nunchuk. Each player can choose to play guitar, bass, drums, or a "frontman" mode that simulates the experience of fronting a band without all that singing. Each instrument is controlled differently in a manner that represents its instrument.
Playing guitar involves strumming the Wiimote up and down while using the Nunchuk's buttons as frets. Playing bass adds movement of the Nunchuk -- you have to twist it as you play, seemingly to simulate raising and lowering the neck. Drumming is exactly what you'd think drumming is: two columns of scrolling markers, and you shake the Wiimote or Nunchuk to match the markers.
"Frontman" mode is interesting. To play as the Frontman, you perform motions in response to onscreen prompts, which are similar to motions performed by singers on stage to excite the crowd. Waving, clapping, pumping your fist ... just not singing!
The motion-based gameplay is not as ridiculous and gimmicky as it may seem. It all works, and it's all fun. The idea of a multiplayer music performance game that doesn't cost over $100 is a good one, as well. Many Wii owners already have multiple Wiimote/Nunchuk combos, and even if they'd have to buy more, those can be used for other games, unlike the specialized instrument controllers.
For people used to Rock Band and the like, Ultimate Band won't really do much. Playing Wiimote guitar doesn't feel as much like playing a real guitar as the Guitar Hero simulacrum, and the music is nowhere near as good, being covers. Disney makes up for the cover aspect somewhat by letting players choose a female or male singing voice, but the cover versions still pale to the originals.
Compared to other music performance games, Ultimate Band is also very, very easy. I played each instrument in either normal or hard mode, and had no significant problems at all. I'm no Guitar Hero expert, either -- I fail pretty early into the hard mode in Guitar Hero. But I could still see Ultimate Band being fun as an activity, even if it's not going to be a challenge. Of course, the demo could have been restricted to the easiest songs, in which case the challenge may in fact appear. In any case, it's more challenging than Wii Music in every way except its ability to challenge your concept of what a video game is.