Regarding movies into musicals:
I don't think that the source of a musical is as important as what the creators do with it.
I know that some people disagree, but I love RAGTIME. It's one of my all time favorite musicals.
On the other hand, I thought that SUNSET BOULEVARD, aside from a couple of terrific songs, was a bore. Like BK, says, "It's like watching the movie on stage". [We saw it in London with Petula Clark, who was great.]
Personally, a good musical is one where I leave the theater humming most of the songs. These days, you're lucky to find one memorable song in a stage musical.
I guess that's why they keep reviving Rogers and Hammerstein.