I'm not sure I can review this book properly, since it's been a while since I read the first three books in the series, but I did like this one. I guess that's the way I feel about all these books: I like them. They don't really jump out at me as extraordinarily brilliant, especially in terms of plot, but the characters are mostly interesting and the writing style is great. The story just flows in a way that makes it an easy read, but not in a simplistic kind of way, and draws you in at the same time. 
 I'm still not entirely sure how I feel about the ending. I liked it, but it still felt too open for my tastes; the fact that (view spoiler)[ Amy saves them all by convincing Dorothy not to commit her very first evil act, after which suddenly no-one remembers her or anything that happened, except for Nox and the fairies, and then Nox turns up in Kansas (hide spoiler)]... I don't know. I would have preferred for Amy to (view spoiler)[ actually kill, or at least defeat, Dorothy. Turning back time always feels too easy to me. Hardship and suffering can't just be erased like that, not even in Oz. (hide spoiler)] 
 Character relationships were nice - Nox and Amy are pretty cute, but I also liked Amy's interactions with Madison and even Dorothy's relationship with her little Munchkin servant and with the Nome King. The scene of the costume ball was very creepy, but in a good way. All in all, it's a good series. I might re-read it at some point to see how I feel about it then.