Gypsy101, by "derivative" work, do you mean that ALW has taken classical themes that aren't currently under copyright (although he may have goofed with the theme from Puccini's "The Girl of the Golden West"
and written variations on them? If so, that's a perfectly respectable thing to do in classical music. People who say he "stole" from Puccini are misusing the word -- it's only stealing when you're supposed to pay. If it's in the public domain, it's fair game. Also, all "jukebox musicals" are derivative, but they're extremely popular. Why zing ALW for writing his own music based on classical themes?
One thing I've noticed about ALW that, IMO, makes him one of the greats is that his shows usually sound different from each other. I am familiar with a lot of ALW's music, but I can't always identify his compositions as his if I haven't heard them before. This makes him quite different from other musical composers. For example, without knowing who had written "Miss Saigon," I listened to the album and knew immediately that it was by Boublil & Schoenberg (sorry, I never remember which one is the composer) because it sounded so much like "Les Miz."
While ALW uses the same themes in a single show, e.g. "All I Ask of You" and "The Music of the Night" are variations on each other, that is common in the musical world, and does not diminish his creativity.
Audrey
Audrey, the Phantom Phanatic, who nonetheless would rather be Jean Valjean, who knew how to make lemonade out of lemons.