Sucks if you just bought GH2 for the xbox360 but the sequel looks like it is worth the money. Biggest change imo is the inclusion of the original artists instead of the cover bands. Songs like Sabotage just couldn't be pulled off by a cover band. The details of online song purchases are not here but I have heard that that will be an included feature for the game. It would be great if the library could spread into the hundreds.
I first played GHII about two weeks back. Nothing like getting drunk and rocking out to Guitar Hero. Fun as hell game.