She was hardly the MVP of THE WIZ, that title rightfully goes to Sharice Williams. Riley has a very charismatic presence that's unlike the majority of those GLEE kids, but I've never thought of her acting as being particularly interesting or deep. To be fair, Jennifer Holliday's TV acting is pretty terrible and she is the definitive Effie, yet I don't see Riley being able to pull off the huge task of succeeding Holliday.
I actually randomly decided to pop in my Blu-Ray of the film this past weekend and while some of the scenes are outstanding, the whole thing just deflates the more it goes on, and the transitions from scene to scene are jarring, not to mention the fact that there isn't a "book" musical number until well into 30 minutes of the movie.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"