This is the first edition of the game to be developed by someone other than Harmonix (they are makign ROCK BAND instead) and I have to say I'm a little disappointed w/ the way Neversoft handled the sequel...
GH3 is not much different that GH2 with the exception of the (kind of lame IMHO) boss-battles. I guess they lived by the "if it ain't broke..." rule, but I would have liked to see SOME innovations in the gameplay.
That said, this game f'ing ROCKS!!
The song-list has some awesome gems in it, and some that are super-fun to play. The wife and I made it through 7 or the 8 stages on Medium w/ 5-stars yesterday and I can't wait to tackle some of these songs on Hard!
The addition of a co-op career mode it great!
I already owned 2 of the guitars, so I haven't yet had a chance to play w/ the New Gibson controller, but I have heard that it is leaps and bounds better than the older versions.