Instruct: Classify a given Amazon review into positive or negative sentiment.
Query: An absolute masterpiece!

I'm surprised to see so many poor reviews. "Wicked" is possibly the best book I've ever read. Gregory Maquire's characters are fantastic and deep. He's created a fantasy world which is just possible enough to be believable and a bit frightening. I'm impressed with his ability to make female characters so real, too. The only problem with this book is that it's so hard to put down; I had a lot of really late nights when reading it. I did not find it difficult to follow at all, although I suspect it isn't an ideal book for someone who doesn't want to do a bit of thinking.