Well my roommate bought this earlier today. I've never played any of the Guitar Hero games, but I liked the concept so I figured I'd give it a shot. I've been playing bass most of the time, and it's a lot of fun. There's a good mix of songs in terms of who gets the "hard part". The character customization is a lot of fun, although I would've liked more short hairstyles. I played the singer for a few songs, and it seems to be pretty accurate in listening to your voice, although I'm pretty sure you can get away with just monosyllabically sing the notes rather than actually singing the lyrics. i also tried the drums for a few songs, and the set plays like your basic drum pad, so good enough.
As a newcomer to the series, I must say that they've made it easy to jump in, and it appears that there's still some difficulty.