I am tinkering in my head with the idea of making a D&D campaign setting based on Oz (A combination of "The Wizard of Oz" and "Wicked" in both book and musical form). Previously thinking it impossible and requiring its own system, I actually think it would work quite well. Let me know what you think of these modifications and feel free to add any you might recommend.
1. All races included but half-orcs, with two races of human: Standard and Winkie. Halflings become Munchkins with the same stats. Elves are tiny and green. Additionally, PC's can play any form of common animal, with the commonly shared stats of +2 Con, -1 Cha, -1 Int and the abilities of low-light vision and reflex save +2. Other changes would have to be made case-by-case.
2. All classes included, although paladins would require a thorough rationale, and monks only for Winkies. The only religions are the Unnamed God and the Pleasure Faith.
3. Female wizards are called witches, obviously.
Opportunities for conflict? Lots. There is of course the war against the WWothW, and prior to that, there is the rise of the Wizard and the subsequent revolts.