I just bought it and am listening to it now. "Roar!" is both monstrous and majestic. I thought that in addition to complementing Cloverfield, that it was a beautiful piece in its own right and a terrific homage to the classic Toho "giant monstah" movies that Cloverfield was inspired by.
Incidentally, the version of "Roar!" that you can download is five minutes longer than the one used in the movie. After listening to both - someone sent me a very clean (i.e. no theatrical noises) copy of the movie's version a few weeks ago - I must say that I prefer the edition from iTunes.
I also got the Cloverfield DVD yesterday. Haven't watched all of it yet but it's a beautiful transfer. I can't wait to put both it and "Roar!" on my iPod... and then I can take Cloverfield with me wherever I go :-)