Setting the story around the Underground Hospital really clicked for me. Larissa's knowledge of medical procedures grounds the story in visceral reality; I have a background in medicine and I appreciated the way the medical aspects of the characters and action helped drive the story.
The two heroes, Eidolon and Tayla, are both characters I liked and admired. This is crucial for me to enjoy erotica, and Larissa balanced "the tragic flaw" against "only I can fix him/her" very well.
Some of the setting was a bit shorthanded, IMHO; I think that Larissa wanted to focus on the key characters and let a lot of details of the world they live in slide. I think it's a little too easy to move around, disguise the "otherworldly" goings-on from the sheeple, and generally live in a world of demons vs. Aegis without interacting with the "normal" world. I can see why Larissa did this, and the story really does shine on it's own without getting bogged down in too many mundane details.
The pacing was very well done, lots of independent conflicts come together at the right points in the book and their resolutions fly as straight as arrow to the final conflict, which turns out exactly like you'd suspect. The denouement seems a little short; there's a few pages where she quickly ties off some loose ends and paints a huge arrow to the unresolved question that will clearly be the basis for Book 2.
The first few pages of the book introduces a fuckton of characters, and honestly I had a difficult time keeping them straight in my head. I'm glad I plowed through it; each of the characters becomes unique shortly and the relationships between them are easy to follow, if not always clear. The murkiness between some of the characters is a product of the balance of competing desires and personalities, and I'm glad this isn't "one for all, all for one" story.
I can wholeheartedly recommend this book to fans of PNR erotica who enjoy action, strong female characters and an interesting and unique setting.