Picked it up today and the game is AWESOME!!!!! the 2 player mode is one of the best 2 player games i have EVER played. You and a friend get to pick between Lead guitar then either bass or Rythm guitar depending on the song and you go at it. If you want to use star power you both have to do it at the same time (which is harder than it sounds )
The selection of songs is great, classic rock, new rock and some hardcore metal. Hanger 18 and Freebird are the hardest songs by far. If you have played the first one, Guitar Hero 2 is a must buy.