At the risk of sounding like a broken record (particularly if one has read any of my other reviews of 40K novels), M. Abnett is easily the most talented writer in the Black Library stable of authors. His works often become canon in the game universe, and much of his writings have formative effects on the latter editions of Games Workshop's Warhammer 40K game, much in the same way that M. Watson's writings did for the earlier editions.
Ravenor, is an excellent action-adventure that utilizes many of the characters introduced in the Eisenhorn Trilogy: Inquisitor Ravenor, Kara Swole, and Harlon Nayl to name a few. M. Abnett also adds a wealth of entirely new cast-members for our entertainment. Ravenor himself is a fascinating character, essentially limited to the realm of his psychic abilities by his physical restrictions. This book clearly delves more into the background of psykers, their abilities, and the interesting physical consequences thereof than any other penned so far.
One of M. Abnett's chief talents lies in creating a vivid, believable setting. The locations sing with the gothic feel of the universe, but from the vibrant view of the privileged and powerful, rather than the teeming, hopeless masses. His characters are bigger than life, but he ensures that there are equally capable antagonists who can match them blow for blow. This contrast provides dynamic tension throughout the work. Unlike some, his villains act intelligently and have believable motivations of their own. Unlike some less capable 40K authors, he makes very little use of dues ex machina and creates resolutions that don't destroy suspension of disbelief.
If M. Abnett has a weakness, it's his endings, during which his plot devices can become a little too abrupt and a little less believable, but this is a minor annoyance in an otherwise excellent whole. It is also clearly the first book in a series, and though it comes to a conclusion of sorts, it leaves most of the bigger questions unanswered, and the characters make plans for future operations in the "last" chapter.
"Fluff"-ologists will love the book, as it covers new ground for psykers and has an abundance of other background material. General science fiction readers will enjoy it on its own merits. There is a worthy sequel already out, Ravenor Returned (which I have also reviewed).
In short: an excellent action thriller which promises to be the start of another trilogy for a fine writer.