Yes-- and I love the book-- but the truth is, it's not a musical adaptation of the book. It's a musical adaptation of the Disney film, which was *inspired* by the book. Disney's traditionally very loose with their interpretations of the original source material (even if the original source is solid history-- see Pocahontas).
Imagine if Disney's "Little Mermaid" on Broadway was true to the Hans Christian Anderson fairy tale rather than the Disney movie. That would involve Prince Eric marrying "Vanessa" and Ariel dying. I don't think that'd go over well with audiences. The truth is, the target audience for Hunchback probably isn't familiar with the original plot of the book. People would go see the show, billed as "Disney's Hunchback of Notre Dame" and bring their children, and be shocked by the violent Quasimodo and Esmerelda's death.
I do feel the show should be darker than the original film, but I feel it should be closer to the film than the Berlin production-- not because it'd be a better show, but because it would attract more audiences.
In my pants, she has burst like the music of angels, the light of the sun! --Marius Pantsmercy