During my Winter break, with a few friends, I got a chance to play the Xbox 360 version of Rock Band. I must say that I am hooked.
If I had some extra cash, I would most definitely purchase the Xbox 360 for that game alone. My weapon of choice was the Guitar, lefty-style like the late Jimi Hendrix. The greatest aspect of the game is that you can play alongside with up to three of your closest friends. It is totally an awesome experience.
One thing that I would like to see implemented in the future, either within this same title or a different version, is the ability to play jazz, country or even hip-hop tracks. That would definitely diversify the title and appeal to other demographics.