Being a guitarist, I find that RB/GH ruined my music not because I now see flashing coloured lights or because it's a horrible concept or I think people should learn how to play real instruments, but because of what it did to song selections.
Whereas before I would either never get requests, or would get requests for some pretty good songs that people might like to hear, now it's a stream of "Hey, can you play Raining Blood? Can you play Cliffs of Dover? Can you play One?"
I'm a blues/rock guitarist, not a metal guitarist, and for another thing, I'm holding a motherfucking acoustic and I don't have a full band backing me! (I have heard these sorts of requests a LOT!)
So yeah, people who seem at first to be knowledgable about the type of music I like, and then turn out to be just reeling off GH tracks.