My wife loves GH but after 2 weeks with Rock Band she says that it is a lot better than GH. She enjoys the ability for us to play together with the different instruments and not just against each other like GH.
You can play cooperative in GH 2 and 80's. That's what we like to do. She usually plays lead guitar and I play bass. She didn't like the Strat controller. She prefers her old GH guitar.
I keep flip-flopping between returning RB or not. I like the game, but I'm hella pissed that they said it would work with other guitars and it doesn't!! Yet the 360 version works with the GH 3 guitar!!! It seems like false advertising to me. They advertised it as being able to play as a whole band, (lead, bass, drums and singer), and on the PS 3 you can't.