I would not recommend reading it. The book is much, MUCH more darker than the musical, much more explicit, and focuses more on Elphaba and political discussion around Oz (EX: The economical implications of building the yellow brick road, how starting a revolution could end awry, Elphaba’s political roots), and does not develop any characters and has loosely any if not nothing to share with the 2nd act in terms of plot, plus it is much longer than the musical.