Figured I might as well add my comments, since everyone else seems to be coming from the long-time Rifts-player perspective. (I'd never even cracked one of the books until I reviewed this one for Leading Edge.)
Overall, I was pretty impressed, and the setting itself sounds fascinating. So much so that I'd be interested in playing it at some point in the future. However, I do wish that they had put the rules first, or at least more forward than they did. Going through the OCC section and not knowing what a single abbreviation meant was more than a tad annoying. (Yes, I could have flipped forward, but I wanted to give it a straight read-though.)
I'm also a bit disappointed that they mention all sorts of DBs and alternate universes, and then don't describe a single one. I know there were space limitations, but I'm pretty sure something could have been trimmed in order to give even just two or three brief examples. I was still left feeling like I only had half of the rules. It's probably enough to play by, but I certainly wouldn't want to GM a game with only the Ultimate Edition.
So that's my two cents. Now to disappear for another three months.