Elfaba is not a nice person at all, just the way she treats her son really upsets me. But her whole character is just very unpleasant, She has to be more sypathetic in the musical. I do think that, if translated straight from the novel, Elphaba would be a character more appropriate to opera.
But she made the novel so fascinating! To me, the whole conceit behind the novel was "The Witch may have been misunderstood, but what does that mean?" Just because she wasn't necessarily "wicked" doesn't mean that she was a pleasant person to be around.
And one of my favorite scenes is after Liir (her son) is discovered in the fishwell, almost dead, and how Elphaba reacts to the situation. She panics, she can't be helpful, Nanny tells her "Oh, you're just like your Mother in a crisis." That was FASCINATING to me!
"Y'know, I think Bertolt Brecht was rolling in his grave."
-Nellie McKay on the 2006 Broadway production of The Threepenny Opera, in which she played Polly Peachum