"Gregory Maguire took some liberties with the story, and what I mean by that is, he fashioned his novel very closely to the movie, however, even the movie deviated from L. Frank Baum's original stories too."
I disagree. It's been a while since I read it (I'm going to start again today), but I wrote a paper on Wicked when it was published, comparing it to both the film and the original Baum story. Maguire's novel follows Baum's story much more closely than the film (but not completely). Since it's been 8 years, my memory is a bit rusty, so I'll refrain from making any more comments until I read it again. I just remember Elphaba as having a strong political agenda.
"What can you expect from a bunch of seitan worshippers?" - Reginald Tresilian