I've argued elsewhere than independent of this project's disappointing execution, Diana Spencer is not really a strong subject for a musical. She has no accessible, understandable goal -- an I Want -- to drive her. She stumbles into the royal family, accommodates her husband's chilliness, 24/7 whine, and betrayal, and looks about for something to occupy and define her. She's mostly putting out fires, not driving herself or a show toward anything with enough specificity. Anastasia connected with many because the character's quest for loving family is knowable and touching. Eva Person, love her or hate her, possessed a compelling raw ambition, reason to follow her for two hours. Even shows that break structural rules require drive, i.e. Bechdel desperately wants to understand her father's closeted life and death; it's an investigation. The creatives of Diana can't decide if the show is a cautionary tragedy or a just -- worst of all -- "a portrait." That's why the character so often stands in the middle of the stage changing clothes while everything swirls around her.
The show's one theme, the abject awfulness of media, would only work if something new could be said about it. But chasing a woman all over the globe until she dies in an accident isn't much of a story, and the aftertaste is sad and bitter.