I probably don't need to say much about this book, as it has gotten tons of publicity. It is an interesting book in which the "Wicked Witch of the West" is given a much more even handed treatment than she ever recieved from L. Frank Baum. Its neat to see some of the questions of good, evil and morality played with using well known fictional characters, and done in an intelligent manner with good dialogue (as opposed to one particular piece of tripe I could mention). As far as I can tell (and I'm a layman, I'll admit), there is plenty of Oz canon used in the book. The map used by the author is the standard canon map. Where I've found it deviates from canon are mostly due to either nitpicking concerns or necessary changes to allow for real shades of gray in the heavily allegorical Oz "good and evil" system.
I think this book is yet another good book that shows why it is important to have Free and/or Open Mythoi available for authors to play with in such ways. This book would never have been published if the Oz world were not public domain. The controllers of the Oz canon would most likely squash this book: it is emphatically more adult oriented, and it makes major changes to major characters.
Speaking of Free and Open Mythoi, I'm working on manifesto of sorts on the subject for Mythoi.com. I'm hoping that I might be able to offer the domain for use as a home to Open and Free Mythoi development.