Rockband introduces guitar solos and BRE's (big rock endings). In which if you're in possession of the rockband strat you can use the top frets without the need to stum the bar to build your points up with great ease (and posturing).
It's also worth pointing out that compared to Guitar Hero 3 the game is quite a big deal easier. While this might be good news to those that struggled even completing medium on that game, to those who finished in the top scores on expert it's a real game shortner. Expert can be compared to Hard and with the exception of some downloadable tracks all but 2 of the 45 standard songs on the disc could be 5 starred on expert first go around.
This doesn't mean that it's easy though, getting high scores on even medium is a real challenge. Expert being near on impossible. In terms of a multiplayer setting, having someone able to sing vocals who might otherwise shy away from drums or guitar is a welcome option.
Luckily the practice mode for drums (as well as the other instruments) is incredibly useful with the option to slow the song down in percentages and in real time rather than just slow & slower. Compared to Rockband, it's a great improvement.
Good: Numerous game options, master tracks, addition of vocals & drums to GH formula.
Bad: Difficulty swings towards the easy side, poor quality peripherals, no online band tour