The Exorcist
The Omen
Children of the Corn
Rosemary's Baby
Invasion of the Body Snatchers (1978)
One must first give up the idea that horror movies are scary. The lights get dark, the soundtrack fades back, perhaps the camera is framed wide or goes seemingly out of focus: a jump scare is sure to come. The real monsters are almost always regular humans. Horror moves in contemporary genre conventions, and if you know the decade the movie was made, you can predict a lot of the beats. (The Omen shares a lot with The Last Wave, and no wonder.) Evil children seem a lot less scary when you know actual children. If you accept the idea that there are nonphysical forces that sometimes might have malicious intent but also that the world is full of strange and random things that happen for no reason, there's really nothing too unusual or to be frightened of. (I do not discount the possibility of malevolent things, but I also don't believe Babylonian demons are doing possession of random people or that Satanic cults are trying to bring about the antichrist for some reason; these scary dimensions just kind of fall flat).
For a long time I've heard people talk about how terrifying The Exorcist is, which left me unprepared for a movie that is almost entirely people talking about problems occurring offscreen. My wife immediately found the feminist angle--young girl going through physical and emotional changes treated by others as a hostile threat--whereas for me it was more about the ability to carry on in faith despite doubts. Contra a common reading of the film, the victory is not hollow but manages to the end of a disaster as well as possible.
Rosemary's Baby, well, I can't believe that guy turned out to be a creep who sexually assaulted powerless women and girls. It's sort of like horror Godard--all that attention to lived female experience, perceptively drawn, but in service of degrading women just because. Still a good film.
Invasion of the Body Snatchers has a somewhat incoherent metaphor at its center--don't think too carefully about what the pods are doing or why, it makes no sense--but really does emphasize how having capital-A Actors and directors committed to a stylish vision and People Who Know How To Make A Movie Look Like A Movie gets you almost the entire way to greatness.