I've always loved the amount of dedication and effort the GH teams have put into their games. You always get a polished feel from the experience, and even after I've mastered nearly all the GH3 tracks (damn you, Dragonforce) I still can't get enough of that game. I've played Rockband with some friends and granted, it IS fun, but god it's a boring game by yourself. None of the individual parts are remotely challenging even on the expert levels. It's a jack of all trades, occupation of many, master of none.
GH4 looks promising too, but they're even starting to irk me off a bit. Exactly how many plastic peripherals am I going to end up having in my room here, guys? Can't you stick with one design for more than one game? I understand I can use the GH3 guitar for GH4, but come on, you know you made the game around the new one's features so if I'm going to get the most bang for my buck, I'm going to have to buy the new model too. Of course I'm getting a drum kit, that's one of the main reasons GH4 has turned me on. Not only does the kit mimic Drummania a bit, but it completely trumps Rockband's pathetically built drum kit (real drummers use cymbals and COVERS).
As far as I know, GH4 comes with the complete band set, the guitar+game, and the game. If there's no drum+game bundle, I'm gonna hold off.