Yes, they're songs we've played before. But not quite...
As you most likely know, GH:SH contains 48 songs pulled from GH1, 2, 3, Rocks The 80's, and one song from Aerosmith. The main difference here is that all the songs are master tracks this time around. So that's really Freddie Mercury singing in "Killer Queen", and that's Ozzy in "Bark at the Moon". The other notable difference lies in the guitar note charts. Every single one hes been redone not only to better accommodate the master tracks, but to update them due to the changes in gameplay since GH1. Also, of course, the biggest addition is the inclusion of bass, drum, and vocal charts, so now you can fail "Through the Fire and Flames" as a group.
Visuals remain about the same as World Tour and Metallica, with exaggerated characters and over the top arenas. This time, the concerts are held in huge "Wonders of the World" areas, and I, for one, think they're awesome. The game also sounds better than it ever has, not just because they're master tracks, but it seems more attention has been paid to the overall mix of each song.
In the end, this latest incarnation of Guitar Hero seems mainly aimed at fans who have been playing GH since the beginning. The only problem is that 48 songs seems a little light. But they're 48 Guitar Hero classics packed in with full band play, so it just might keep you busy longer than you think.
P.S. Good luck on "Free Bird", its tougher this time.