Just got back from E3. Rock Band 2 was awesome - spent about an hour today playing around with the new instruments and the new songs.
The new drums are nice and I noticed another mini-jack connector in the back (for the cymbals or a second pedal?) The pads are noticeably improved as well.
The new guitar is nice, I noticed the light sensor, but couldn't find the microphone. The strumbar is IMHO halfway between a GH guitar and a Rock Band guitar - no clicking, but not nearly as mushy as the RB1 guitars - it felt more substantial than the old guitars.
I ended up singing (poorly) for most of my playtime since no one else wanted to sing.
I might have ended up on someone's video, who knows.
Other than that, I dunno what else to say, it's Rock Band, it kicks ass, and the new songs are fun