As someone who was a little skeptical about the premise for Rogue Trader, I have myself drawn into this game (though my true preference lies with Dark Heresy).
This sourcebook however, is one that I'll be placing a hardcover order for as well. There is a true wealth of information and ideas in this book that make it a must for your collection. I'll be using some of this material in my Dark Heresy game (Force Weapons, anyone?), but the fluff is well-written and relevant, and the rules a good compliment to the existing product line.
The one fault I can find is one of personal taste. In deciding to showcase the first two non-human Career Paths, how did they settle on Orks and Kroot. I can see the attraction to the Kroot, but I really don't see the Ork as having character longevity. I would have preferred that they focus on the other nearer-human races instead - but as I said, it is a matter of personal taste.
In short, well worth the dollars.
[4 of 5 Stars!]