Holly Black isn't writing about the clean-cut honor roll students, the ones who most YA authors want to write about. Her teens are the ones that are falling through the cracks. It is this that at the very outset grabbed my attention.
In Black's faery world, things are much more like the original Grimm tales, updated for a modern sensibility. Faeries are capricious and often cruel, with little to no understanding of consequences or the suffering of their victims.
The central love story is pleasantly understated, and allows for generous character development between Kaye and the dark faery knight whom she rescues.
The writing style is definitely aimed at teens, but respects that teens are much more knowledgeable on certain subjects than most authors and publishers seem willing to acknowledge. Black does not shy away from hard subjects, and does not hesitate to put her characters through the wringer. The world she's created is hard, and no one in it gets an easy ride. That alone made this a compulsive page-turner, because she makes it quite clear that what happens within her pages really truly matters. I finished it within the span of a day.