Wow, this post has made me completly change my mind about Rock Band, I wasn't planning on getting either RB or GHIII. However, after several positive comments abouot RB and this thread I'm really considering it.
Especially when I have gaming sessions with all my friends, usually we're competing in Halo or Warhawk or something. Rock Band looks like it could be a refreshing change after several rounds of Call of Duty.