Rock band is the first music game to allow players to play all 4 parts of a band. From drums to bass, from guitar to singing, the possibilities are endless. As long as they're one of those 4 parts. But 4 is enough. Especially when space is a premium.
Anyways, the instruments are fun. The guitars are bigger to give you the more realistic feel compared to other fake guitar games. The drums are noisy but still a whole lot of fun. They have more a real feel than you get from playing the fake guitar.
The music in this game is good too. Lots of classic hits that you know and love are here for you to play and love. It only comes with 58 (great) songs on disc but Harmonix (the developers) keep updating your music options by allowing you do download new songs each and every week. This makes the replayability of Rock Band less because you'll have new songs to play! Hooray.
All in all, Rock Band is the greatest music/rhythm game to date and is lots of fun, especially in groups.