I think THE WIZ has one of the worst books for a Tony-winning Best Musical in the history of the awards. The score has some wonderful music, but that book is really bad. Wisely, even though the show won 7 Tonys, Best Book wasn't one of them. SHENANDOAH rightly won Best Book that year.
The film is just awful in every respect. Ted Ross, who won the Tony playing the Lion, is the only one who stands out among the four principals. Of course, Mabel King as Evilene is lots of fun, too.
I saw this movie opening weekend in a theater whose audience was 98% African-American, and they were rapturous with every song and production number. I thought the roof was coming off the theater with "No Bad News," and Horne's "If You Believe" and Ross' "Home" got STANDING OVATIONS! I just sat still and cringed at how deadly the film was paced.