'Diana,' as directed by Christopher Ashley, has on display. The real problem is intrinsic, arising from the choice to tell the story in song at all. Musicals, like laws, are often compared to sausages: You don't want to know what goes into them. In this case, you don't want to know what comes out, either; if you care about Diana as a human being, or dignity as a concept, you will find this treatment of her life both aesthetically and morally mortifying.