I'm surprised at all the negative reactions to the newest book in the DH line. I have been waiting for Ascension for a long time (I pre-ordered it last June I think) and I'm quite happy to have finally got my hands on it. I have been playing DH since it came out. I'm currently running a game (1-2 times a week), playing in a game (1-2 times a week), and running a Rogue Trader game nearly once a week (my schedule will get even crazier when Deathwatch comes out). I think the long wait for the book had people expecting something they didn't get. To be honest I didn't have expectations beyond it would be a book allowing me to advance characters up to the interrogators and inquisitors and have a handful of other paths and cool advanced skills/talents/gear etc.
To be honest I haven't had time to read the book cover to cover, but what I have seen and read I'm really excited about. The people I play with are also very excited (and have read more than I have). When I first heard about a 40K rpg I was skeptical, but I think what has been done so far is great. When FFG took over I was worried, but they've done an awesome job.
My only complaints with any of the DH/RT line is some editing errors which have been addressed in errata, the lack of a good index in the IH, and some of the layout of the adventures (which can be taken care of by me making my own notes).
I think the book is great, I just wish I had it in my hands sooner (my wife's character is at 24,000 and has been itching to ascend to interrogator for months).