What makes a "good" topic for a musical?

I see so many posts that say this or that idea is a bad idea for a musical (ie. Lestat, Mask, Legally Blonde) What elements should be necessary? Why are some stories, movies, books, etc. better than others as a foundation for a musical? Can anyone list the things that an idea must be or have to be considered a "good choice" for a musical?

---

I second that. There are certain things that "sing" more obivously, and things that have certain issues that would have to be addressed, but that's on a case by case basis. There are really no rules that can or should be made about the musicalization of a property.

In today's world though, where artisticly initiated musicals are an endangered species (I'm talking everything from Chaperone to Awakening), producer initiated musicals (and even artisticly initiated musicals with commercial clout) are treated with extra suspicion.

---