Loved Mellie, loved the set-up (chubby kid teased since kindergarten for her youthful belief in fairies...which, of course, turns out to be true). Mellie is a terrific narrator, and as the fairy world becomes more visible (and creepy) there are a lot of cool set pieces and images. The pathetic and drunk yet proud fairy that Mellie and her family encounter at their grandfather's old inn is a terrific character. And I found the ending super-satisfying.
The problem: I was bored senseless by all the fairy politics and tools and rules of fairyland. I think this is one of those situations in which if you're already a big fantasy fan you won't have any problem with this, but it was like watching fairy C-Span for me.
FWIW: for moms of girls: I think from a body-image standpoint this is a SUPERB book. People are douchey to Mellie because she's pudgy, and the portrait of bullying is harsh. Ultimately, Mellie's resilience is awesome and her problems are solved not by her becoming skinny, but rather by her developing a spine and some trust that not *everyone* is a dickwad.