I got an achievement for syncing the guitar to the TV :)
I didn't buy this, but @QforQ brought it over to my house for a gamerDNA gathering... we jammed out pretty hard to this. I had a good time, but was hampered by my lack of beatles knowledge. The multiple mics is lots of fun... the general rule, is that if you can make it so that more and more people can play the Rock Band games... that is a win. The fact that people can just join the singing in multiple numbers makes it much easier for people to play because they can sing along with others and not have to carry the whole show.
Harmonix continues to do some interesting things with music games... although in general the game still feels the same. The entire genre is going to need a revolution.