I read the book. I saw the musical. Now I think about it constantly...
As an alternative history is an interesting option.
As a prequel to "The Wonderful Wizard of Oz" - not necessarily, because it's a mix of book and movie (1939) and there is a few of inaccuracies.
The book is specific, depressive and more serious. Musical is incredibly joyful and colorful. But first and second thing complement each other, so both are worth knowing.
SAI, PS CS + Volito2
My other work wit OZ here: [link]