Great book. Have you read Wicked? You should. There is another book from Gregory Maguire I have not read: A Lion Among Men. It's the third in his Oz series and seems to be a flashback story. But Son of a Witch also lends itself to another book about the witch, so I hope he's writing it!
Now I want to read L. Frank Baum's books of Oz, because I 've only seen the movies and Maguire references lots of things from Baum's world of Oz. Has anyone read these books?