Probably for Metallica fans only, although there is some real GH shredding goodness in it.
The licks were challenging, even on Easy (at least personally) but that kept me engaged. I'm not sure there is going to be much of a replayability factor for me once I've worked my way through the entire Metallica catalog. I think there are some nice animations along the way, nothing ground breaking, but it is nice to see the guys in graphical form rocking to the tunes as you jam with them. Although, I gotta admit, it's tough to follow the animations when shredding through some of the faster solos. Frantic and Creeping Death are two personal favorites.
Where Guitar Hero III was an event, this is merely a fanboy's collection. I'll try out Aerosmith's, but I don't think I would take a jump into any of the other sequels and add-ons after experiencing this game. Don't get me wrong; it was fun. But I'm thinking that's because of the 20 years I've given to the band. The more I play it the more I enjoy thrashing to the tunes. And after playing Aerosmith's GH, I notice all the little bells and whistles to this version of the game. It does seem more sophisticated but not to the point where I think anything is ground-breaking.