First, a couple clarifications. This is actually two novellas, Infected and Prey, rather than one long novel. Also, there is no sex in this book (though it's very much M/M), but that didn't actually bother me at all. 
 I spent most of my reading time with Infected: Prey thinking about how great it almost was but wasn't quite. I actually put it down for a couple weeks in the middle of the first novella and felt no particular compulsion to return to it, though in the end I'm glad I did. Andrea crafts a fascinating world, and though I've not read too many shifter books, I've seen enough of it in pop culture to say safely that her concept of the shifter felt quite unique to me. The infecteds live a brutal and unglamorous life and constantly battle both the impression that this isn't the case, and widespread hatred. Shifting is a disease spread by sexual or blood contact, much like AIDS. Also much like AIDS, it's an eventual death sentence (the stress of shifting eventually kills people), it carries a huge social stigma, people blame "the gays" for it, and children can even be born with it via infected mothers. It's a wonderful social commentary, subtle enough not to leave you feeling bludgeoned over the head, clear enough that you can't miss it. 
 My single biggest issue with these novellas was the writing itself. The author could really have done with a stronger editorial hand, for while her writing in general is solid, she is also extremely prone to tangents and repetition. I actually came to dread the introduction of new characters, because every single one, no matter how minor (random prostitute on the street, random barista behind a counter, you name it), got full descriptive treatment, generally several sentences long and almost universally pointless. I don't need precise physical descriptions of every person to wander on and off the page. And it happened so often that it really killed the pacing. I also thought the intro to the first novella was pretty weak (it was told from the POV of a minor character and meant to set up the mystery, but failed to draw me in), though by the end of the first novella, I didn't want to put it down. The weaving of the mystery in Infected was beautiful, the ending perfect, and the character development for Roan left me hungry to see what would happen next. 
 Prey starts off much stronger than Infected did, drawing me in right away. Again, it was told from the POV of a character about to be murdered, but it was much smoother, and even in her few short pages of life I was made to care about her. The pace of Prey was also much smoother and faster than Infected, the writing overall felt stronger, and while the glut of character description was still there, there were fewer random tangents where the author just went off and wrote a page about something completely irrelevant to the story. Overall I enjoyed Prey much more than Infected from a craft perspective, as if the author had really grown as a writer between the two pieces. Alas, I did have trouble keeping all the names straight in Prey--there was a big cast of characters involved in the unfurling of the mystery, and the author used their first and last names interchangeably, which made it very hard to keep track of who was who; just when I thought I remembered who one guy was, she'd call him by another name and I'd have to flip back and figure it out all over again. Still, there was a very satisfying conclusion to the mystery in the end. Despite that, the book ends on a distinct downer--an HFN at best--that felt kind of unnecessary to me, a bit like the author made the conscious decision to kick us in the teeth at the end. I respect that, from a craft perspective, it's not always realistic to have an HEA, and presumably the author made a conscious choice to remind us that even with the mystery solved it's not all rainbows and puppies. But in this particular case, I don't personally think that an HEA or an unblemished HFN would have affected the integrity of the story, and the ending as it's written left a very sour taste in my mouth. 
 That being said, if she writes more of Paris and Roan, I'll be reading it. The worldbuilding was wonderful, the characters multilayered, and Andrea makes us care about them deeply. Though there's quite a bit of ugliness in her world, and reasons to be depressed, there's also the kind of loving relationship that we could all only dream of, and some really fabulous humor, especially from Roan, the super-cynical detective at the heart of the books. (Favorite line? "There were so many good reasons for hating people on an individual basis that mass, generic hatred seemed idiotic. Hate a person for who they were, God knows he did, but for what they were? Moronic and lazy.") 
 If GR had half stars, I'd have given this one 3.5. If the editing had been sharper, I'd have given it 4, maybe even more; it's hard to tell how much more deeply I might have found myself sucked into the world if all the pacing problems hadn't gotten in the way, but I suspect the answer is "quite a bit." If you're not bothered by that sort of thing, and you love strong worldbuilding and strong characterization sexy shifters, you will almost certainly LOVE this book. Even if you are bothered by that kind of thing but love worldbuilding and characterization and shifters, you will almost certainly quite like the book. Read it and find out for yourself :)