Sally Jane Bruce gets a hard time from people used to the slick emoting of millenial stage kids.
I think that her weird line readings and (plain bad acting) add to the oddness of this story.
As a film from the golden age this has aged very well. In terms of the religious critique and adult-child relations, Laughton and Grubb's novel skewers the hypocrisy that existed in society and both Bruce and Chapin are more interesting than the pieces of code standing in for human beings as Wanda's kids in Doctor Strange.