This book kinda snuck up on me. Early on I had it pegged as mostly porn - the writing is fairly simple and it is on the smutty side. But there's a story there as well, and the further I read, the better the story got, and the writing seemed to me to get better and better in the second half of the book too.
This is not really a darkfic, so much as an adventure story, with a slave, fallen angels, a militant church, and a prince battling for his crown against evil usurpers. Good fun, and very enjoyable.