The longest in the series so far, and the best as well, chronicling Fulgrim's tragic fall from grace. It is action packed, well written and exhaustingly detailed.
Strikingly it seem's to draw heavily on influences from "The Picture of Dorian Gray," from the descent into grotesque hedonism, the influence of a piece of controversial literature (although not the same piece), murders disguised by dissolving the bodies in acid and a picture, that has disturbing qualities.
It inevitably suffers in comparison with Wilde although it is by itself excellently written. It also suffers, unfairly, in that many will already know the end of the story (although this is by no means the fault of the author).
It is however, a gripping read, smooth, fantastically detailed and at times genuinely moving. If you are a regular visitor to the hall's of the Black Library then this is a must, and if you aren't familiar then this is as good an introduction as any.
My only real criticism is that the end feels a bit rushed (or perhaps compressed). The first half is given over to a meticulous account of the corruption, whilst the second half (in the same amount of pages) deals with a vast amount more. The result is a book feeling slightly lopsided.
This is a minor failing though and overall the book is excellent.