I first saw this movie at one of the local movie theaters around Times Square, New York, that frequently featured second run British movies.
My original intention was to see James Mason and Stewart Granger face off against each other. Instead, I found myself falling in love with the heroine played by Phyllis Calvert, who immediately became my favorite British actress.
The story may smack of soap opera; I've followed several in my time, and yet this story, admittedly overdone, I found to be very sympathetic, and immediately found myself falling in with the main protagonist, and wishing her to eventually prevail, despite all the adversity she had to face from so many individuals.
I have continued to love this movie and have gone back to seeing it many times. I admit that Stewart Granger is rather wooden at times and James Mason appears only at certain strategic moments. However, the player whom I found myself yearning more to see was Jean Kent; fortunately for her, she was given full opportunity to display her complete diversity in subsequent films, many of which I have also seen. (I would like to comment that Ms. Kent is happily still with us, approaching 90 as of next year.)
I agree that the moment where Stuart Lindsell as Fanny's natural father is about to kill himself because of pressures exerted by his erstwhile wife having become too much is right out of a horror story, at the moment where one sees those multiple mirror images.
Certain other players in this film I have also found to be quite believable considering the context - Wilfrid Lawson as Chunks, Amy Veness as Mrs. Heaviside, and perhaps one or two others.
In addition to James Mason, the individual contributions by Margaretta Scott and Cathleen Nesbitt are also sufficiently believable to invite our intense dislike, as each throwing another obstacle in the path of our heroine.
I understand that these impressions are purely individual; as with any work of art, we experience such in our own way. In my case, it made a very warm, positive impression on me - I cannot say exactly why. I would recommend it to anyone who likes high Victorian melodrama, mindful that I am not necessarily in a majority with my impression, but that is how I am. Chacun e son gout, as they say.
I just finished viewing Madonna of the Seven Moons, another film in this same Gainsborough series, and also featuring Phyllis Calvert, Jean Kent,and Stewart Granger. While this latter is a fascinating story based upon a multiple personality, I found it to be inferior in its cohesiveness and ability to draw the viewer in, compared with Fanny by Gaslight, which I have just commented on. I could easily imagine that the superior direction by Anthony Asquith may have something to do with it.