Step 1: expect sociology, not horror.
Step 2: Imagine a world before Kinsey spread the lie that everybody is really, secretly a pervert. Two of the bad things about those days (which were far saner sexually, than now, regardless) was the inability of people to talk about anything sexual, and the expression of sexism and misogyny through putting white women in well appointed suburban cages. (Now, all women are at equal risk of being treated like disposable meat; not an improvement, but it's different.)
Step 3: Read "The Yellow Wallpaper" and the associated cliff notes.
Step 4: Watch movie, and try to see things from her point of view. Yeah, the symbolism is about as subtle as a volcano, but you really get to see the late 60s/early 70s mind set.