I bought this book after reading about it on Unshelved - it sounded too good to pass up, and I'm so glad I picked it up. I was a little wary about a book that focused on characters playing musical instruments (I'm a musical dunce, despite living with musicologists), but Stiefvater's mythology employed music in a way that was entirely engaging and required absolutely no knowledge, understanding, or affinity for it.
What I loved about this book is it's a fairy tale that's not afraid of how truly nasty faeries are mythologically. The faerie aspects of the story unfold slowly, so for a large part of the novel there's just a suspenseful sense of faerie menace. There are so many wonderfully evil characters that I wanted to bask in the feelings of danger. While sometimes I've felt that I've read too many stories about faeries at the moment, this book didn't make me feel this way - it withheld the answers to the end so much that I HAD to keep reading.
My one complaint is that this book felt like it ended really abruptly - I would have liked to see a little more wrap-up and clean-up at the end. There's a sequel, Ballad, coming out in October, but in the meantime, there are so many more things I want to know! But if you can handle not having all of your questions answered, this is a great book that was suspenseful without being scary. I'd say it's like Holly Black's Tithe series with more drama and fewer answers.