Ok, folks, as a man who has listened to the concert cast recording to the point of oblivion, read the novelization, and seen the movie three times, here are the differences:
BEWARE SPOILERS!!!!!!!!!!!!!
The talent contest takes place at a theatre in Detroit as opposed to the Apollo Theatre in New York.
The following characters appear in the movie that don't appear in the musical:
Effie and C.C.'s dad
Curtis's aunt Edith and his sisters
Deena's mom (although she is mentioned and Deena has a telephone conversation with her)
Magic, Effie's daughter (although she is mentioned too)
Jimmy's wife, Melba
Max (played by the amazing Ken Page. Listen, folks, don't cast Ken Page in a movie if he isn't gonna sing!!!!!!!)
Curtis's record label does not have a name in the show.
The movie expands upon the historical background of the time period. For example, the Dreams are recording Heavy, Heavy as the Detroit Riots of '67 rage on outside.
In the musical, we have to assume that this is both Deena and Curtis's first marriage. In the movie, Curtis says he has been married before.
Curtis does not try to make Cleopatra in the show. He simply says, "I don't want you doing that movie, period."
Deena's mother dies in the musical.
In the musical, the only thing that dies concerning Jimmy is his career.
In the musical, Michelle makes no mention of a brother.
In the movie, Michelle is hired as a secretary for Rainbow Records. In the show, she seems to be an already established vocalist who was picked out of a lineup.
In the movie, the death of Jimmy's career is not at a Democratic Fundraiser (by the way, go Democrats!!!!) but at a tribute concert for Rainbow Records.
Jimmy shows no signs of being a drug addict.
Deena does not tell Effie about Curtis's illegal dealings. Marty and C.C. fess up to Effie's lawyer.
Curtis never tells Deena, "your voice has no personality."
There are no private meetings by the pool.
I'll be back with more differences when I think of them.
Butters, go buy World of Warcraft, install it on your computer, and join the online sensation before we all murder you.
--Cartman: South Park
ATTENTION FANS: I will be played by James Barbour in the upcoming musical, "BroadwayWorld: The Musical."