I didn't find the central mystery very engaging, and I figured it out by being genre-savvy rather than following the clues, which is eh. This is about my only complaint in the book. I enjoyed the relationships between the teenage main character and the adults around him, which were an excellent mix of "adults providing guidance" and "adults actually listening" with a dash of "adults being clueless" that was always understandable in context. In general, I loved that the teenager would (a) share his suspicions with sensible adults and (b) the adults would respond in a serious manner. The story is set at a school and you get the sense of faculty and student working together to help the student achieve his academic goals, and I found that enjoyable and authentic. The relationship between the main character and the other teenage protagonist was also well-handled, including some friction at the start not only to create interest but to establish the characters, and then allowing a believable friendship to develop out of it. The book has two climaxes; the later one feels almost like an afterthought and doesn't really involve the main plot, but is nonetheless brilliant.
The central mystery is a series of abductions/possible murders, but the tone is more light-hearted than that would suggest. If you've been avoiding the other Sanderson series that I've recommended because they sound too grim, this would be a good one to start with. The world as a whole seems like an interesting place to live and one that's pleasant for most of its inhabitants. I'll give the book a 9.