I'm really being generous here. I am a super fan of both the GH and Rock Band series and I am aware that Harmonix birthed both. I knew the story would be stupid, everyone one did, but GH just did what they do best since GH 3, make the game easier and more ludicrous. For expert players like myself this is just new songs for us to sightread nothing more and nothing honestly new innovated into the gameplay like what Rock Band 3 is doing. This series I'd say has one more title left as they have to copy Harmonix and add their keyboards and their version of Pro mode and by then honestly I won't care. I won't buy a second keyboard and a different MIDI guitar controller for another GH. Harmonix beat them. 

P.S. I also won't be surprised if RB3 is the last legit (meaning non-band oriented unlike Beatles RB). I don't see how they can innovate this genre any further. Besides all they need to do is keep adding weekly DLC.