I purchased this book largely on the strength of Amazon readers' reviews, and I was disappointed. I can only assume that most of the reviewers were young (perhaps reviewers should be required to give their ages). What I found stimulating as a teen would not make my current late 20's reading list, and this book isn't in the four-to-five star range. I would consider it slightly better than average.
Comparisons with Tanya Huff and Laurell K. Hamilton are inescapable. Huff and Hamilton both feature strong female protagonists involved with vampiric lovers. In particular, Lackey's characters pale beside Hamilton's Anita Blake and her French vampire consort Jean Claude. Lackey's characters lack depth. A reader would be hard pressed to describe Di or Andre outside of this novel's particular plot conventions, while Hamilton's Anita and Jean Claude are life-like, down to mannerisms and speech patterns. Hamilton and Huff's characters are witty, sharp, and sexually potent. I was disappointed by the tactful omission of the sex scenes between Di and Andre. While Lackey is progressive enough to feature a gay male couple, apparently grown-up sex is still too risqué. As for the assertion that this novel is "realistic", Lackey's Di (able to defeat demons and protect the general populace), when desperately in need of a gun, has apparently never heard of a "credit card." Realism, this is not.
In conclusion, this is decently-written fluff, but not comparable to the works of the better female authors of this sci-fi/horror genre.