There are a lot of complaints about the rock songs on this album, but most of them sounded fine to me. (We can X Hoobastank, since it really doesn't seem to have anything to do with the game, soundwise or not.) Save for that one, last track, I love the rest of the CD. "Follow" by Incubus is one song that I repeat all the time... in fact, it was that song that pushed me over the edge and made me buy the soundtrack. Hearing it in-game was a blast. (It's IN-game, so it is part of the game soundtrack, not just added in.)
The "problem" here is not that there is rock on the album: Halo is changing, this game is more intense than the first, and from what I've played, I like the new sound. It can't always be just Marty, and the fact that some big bands contributed to the album really shouldn't be that big of a deal. I have tremendous respect for Incubus, actually, because they composed four different pieces of music for the game, most of them over five minutes in length. (By the way, think it's too long? Think of it like a symphony... then it makes sense.)
My only real complaint is Hoobastank's song. I don't really like it. And "Never Surrender" throws me off a bit after listening to beautiful orchestral scores and intimidating rock songs--you want to talk about being out of place on an album? ^^;