Maybe it was the lack of love triangle, the multi-faceted nature of Chimeras, the beautiful descriptions of Prague and Marrakesh, or the way that Karou's history was revealed almost in reverse, making me think (if very superficially) of Memento; I'm not sure exactly what it was about this book, but I was completely engrossed.
Taylor does a wonderful job of drawing you in with little bits and pieces, hints of what is to come intermingled with hints of what had already came to be, so that at the end you come to understand Karou, and the fantasy world she half-resides in, almost completely.
The love story is beautiful and heartbreaking, the settings and physical descriptions vivid. The story takes a little time to really start, making it feel slow at the beginning, but once it does pick up, it's more than worth the slight sluggishness.
The only thing that was really missing to me was a concrete origin story, for lack of a better phrase, of the Angels and the Chimera and their world.
But that's what the sequel is for, and, unlike some recent YA books that should have quit while they were ahead (I'm very sadly looking at you Cassie Clare), I'm really looking forward to what else can come of this trilogy.