Outstanding. Truly, truly outstanding.
I will preface this review by admitting a bias. I have a certain penchant for the subject matter, having been fascinated by Dante, Milton, and others who have dealt with Hell before. Given that, I can say with confidence that this is the most "personal" treatment of Hell that I've ever read.
Barlowe captures the essence of supreme sorrow that most typifies what I envision to be the greatest anguish in Hell. By humanizing the protagonist (a Demon) to a certain extent, Barlowe allows the reader to share in the sense of loss and pain that came with the Fall. Nevertheless, Barlowe is eloquent enough with his text that the "alien" nature of the characters is never lost.
There are very few flaws in the work (and I reviewed an Advance Review Copy, so some of them may have been altered in the production release), but I will try to touch on them.
The timeline of the piece can be a bit confusing at times, with the passage of time too often going unsaid (or, at best, loosely implied). Now, it may well be unfair of me to make that statement, as it is true that there is the notion that time itself (at least to the Damned) becomes meaningless in Hell... and Eternity is more than just a "very long time"... Still, as a reader, reading a book with a plot, there were times that I felt that I'd "missed" something and had to flip back (sometimes several chapters) to double-check the timing of an event or discussion. That said, the immersive nature of the narration far outweighs any minor inconvenience in being momentarily confused.
There are many characters, of major importance to the plot that have "similar" names. Again, in all fairness, the nature of the characters requires a certain creativity in naming... but as a reader, sometimes I found myself having to remind myself which demon was which... particularly the ones whose names start with the letter 'A'.
There is a "reveal" at one stage in the novel that, while certainly not obviously telegraphed, was not quite the surprise to me that I felt it ought to be. I do not wish to spoil the plot for the readers, but it revolves around a main character and his/her past. That said, the fact that it wasn't a surprise did not spoil the PLOT any nor ruin my overall enjoyment of the work. I almost feel silly for complaining about it... in fact, it's not even really a "fault" in the work.
Lastly, I did find that there were times when the text seems to take for granted that the reader has specific knowledge of the history/culture/mechanics of Hell that I do not feel are adequately set out beforehand. I understand that this is actually a legitimate literary technique and (to a certain extent) is even REQUIRED by the frame tale of the narration, but it still can be a bit jarring when the reader is forced to read several pages without fully understanding what is happening until later. I think that this might be somewhat obviated by perusing Barlowe's "sister" works Inferno and Brushfire, which deal with similar subject matter, but I did not do so prior to reading the novel.
Regardless of the fact that I've taken up the bulk of the review by discussing flaws in the novel, I've given the work 5 stars. I feel that there are few works in human history that are without any flaws, and the minor flaws here are WELL outweighed by the beautiful and moving text. Barlowe has really created something special in this novel. I hesitate to call it a "masterpiece"... only history should make that judgment. I do not, however, hesitate in saying that the Commedia and Paradise Lost find themselves in excellent company with God's Demon.