As an avid music fan and video game player, I have to say Guitar Hero fosters an interest in music not musicianship.
It simply isn't possible to listen to a song 14 times and not either begin to like it or get curious about the band's other works. Kool Thing
doesn't jump in sales without a reason.
The game Rock Band, is slightly different. While it still has the unrealistic guitar and bass playing, vocals and drumming take a very real skill or at least raw potential. I would have loved the chance to play along with Kiss when I was a kid.