Maguire based his novel on L. Frank Baum's original Oz stories while the Broadway show is more inspired by the classic musical motion picture of 1939. While both book and play have political subtext, the novel is much darker while the musical is a lot more light-hearted. There are many differences between Maguire's tome and the Stephen Schwartz and Winnie Holtzman Broadway adaptation.
Since the musical continues to become a mainstream sensation, I am glad that the ABC network (and Disney, its parent company) are bringing the novel to life in a more faithful version. If the mini-series is a success, maybe we will see versions of Maguire's other books in the Wicked series: Son of a Witch and A Lion Among Men.
The mini-series is being produced by ABC Studios and Salma Hayek's Ventanarosa Productions.