For comparison's sake, my husband and I re-watched the original Gloria Swanson film last night. Swanson played the character like a madwoman right from the start, where the musical seems to depict her more as deteriorating over time, which I found more sympathetic.
It had been many years since we'd seen the film and I was surprised by how flat the last 10-15 minutes felt to me. Beginning with "the phone call", the proceedings felt relatively low-key and lacking in dramatic tension compared to the musical. When Betty arrived at the house, the interaction between she and Joe appeared almost playful at times; he didn't seem as bitter and disgusted with himself as the character does in the stage production. To Andrew Lloyd Webber's credit, the scoring of the musical at this point is far more threatening and fraught, and makes for a more compelling finale.
Also, I noticed that the film places the thunderstorm on New Year's Eve, where the musical (if I recall correctly) moves it to the final scene, which again serves to heighten the tension of the sequence.
I even found Norma's final descent of the staircase (and into complete madness) less gripping and engaging than in the musical. I didn't feel for Ms. Swanson's Norma at this point like I did for Ms. Close's character. Both are at times funny due to the inherent camp factor, but with the stage show my reaction oscillated between amused and heartbroken.
==> this board is a nest of vipers <==
"Michael Riedel...The Perez Hilton of the New York Theatre scene"
- Craig Hepworth, What's On Stage