I enjoyed looking for things that were different from the Judy Garland movie. One of my favorites is that Dorothy’s shoes were originally silver, but were changed to the famous ruby slippers for the movie, presumably because silver would flash too much and not show up as well, and to take advantage of the brand new innovation of color in film.
Fans of the Oz books are legion. If you want to read them all there are 15 by Baum (the original author), 19 by Thompson, and about 134 books in all (credit goes to KidLit Club member CIARRAINIC for this information).