Excerpts:
GN: The main new thing in Guitar Hero II is the ability to play separate lead, rhythm and bass tracks, or segments of the song at least...
JT: Yeah, let me explain that. People are really excited about the game, but after playing the first game and being used to it and getting through to expert mode, people just wanted more, and so we knew that for the sequel, "more" means a lot of things. It's not just more music, or more characters or venues, they want to have the full experience filled out. In Guitar Hero 1 you're playing just one stream [of audio], and in co-op mode, you're actually sharing that stream and it alternates back and forth and you share the two channels, the left and right channels. But it's really just one stream that comes off the disc, the lead guitar.
For the sequel, for every song, there's going to be two streams. Some of those second streams are going to be rhythm guitar, and some of those streams are going to be bass guitar. So there's not three streams, there's actually two streams. But with two guitars you'll actually be able to play co-operatively and you're not playing the same exact track, like sharing the lead guitar track. You're actually playing your own track.
...IGN: What sort of stuff did you have to cut from the first game that's making its way into the sequel?
JT: There's the practice mode, the ability to go in and pick a section and loop it. I mentioned, for multiplayer, picking separate difficulty levels... so those are the things we're getting in.
In terms of content, I mentioned more, so we're talking about venues, characters, stuff like that - we're definitely touching everything and giving players more... more to experience. And obviously, if you're playing a bass track, we're going to be looking at including bass guitars into the game as well.
Well, I'm good. I wanted practice mode (in), different roles in multiplayer, and a load songs (there will be 55). I'm still playing this game almost every day, believe it or not, and I think it's been at least four months now. That's how ridiculously fun it is.
Here's the link to the full article:
Guitar Hero 2 interview