This book is extremely enjoyable!
The characters are developed quite nicely, and their progression throughout the book is realistic. Maddy grows to be more comfortable in her skin, which is respectable since she's so young, and though her personal characteristics never change. Gareth is already sure of himself, but the author STILL manages to help him develop and grow in other respects.
The plotline is well thought out: no plot holes or glaring inconsistancies. The main focus of it is simply amazing, and the supernatural world she develops is unique and intriguing--not a run of the mill "let's stick with cliche" or something equally boring and ridiculous.
I highly recommend this!