I have to say that I have no idea why the publisher would promote this specifically as a young adult book. It's not that I don't think certain teens would love it (I do), but it seems to me like the kind of book that would appeal to a certain kind of reader as opposed to a reader of a certain age. I would love to hear from teens who liked it, and for them to tell me specifically what they liked about it.
Midwinterblood reminded me a bit of Meg Rosoff's book The Bride's Farewell (one of my faves the year it was published), or of Far Far Away by Tom McNeal, not so much for the specific story as for the feel of it--old, legendary, fey. I look forward to reading others of Sedgwick's books.