Verdict:

Suspense and subtlety are these are this movie’s main strengths for most of its runtime. It’s slowly and carefully carrying a tray full of crystal glasses. Every element feels meticulously crafted, with small, subtle clues keeping the audience on top of what’s going on. There are no loud screams or startling sounds. The movie continues to carefully carry this metaphorical tray until the end and then…it just drops and smashes everything onto the ground with its comically ridiculous ending.
Although this film laid the groundwork for modern horror movies, it is in many ways the opposite of those movies, because it is not a horror movie. It is not even a thriller. Instead, it is a mystical psychological drama and, boy, is it a slow burn. While this restrained approach may appeal to some, many viewers expecting a more traditional suspense-driven experience may find this movie tedious. The person I was watching it with left halfway out of boredom, and I completely understand.
At least, before that happened, we had a few laughs about the over-the-top acting. The dialogue writing for the main character was rather poor as well. The dialogue, especially for the main character, was rather poorly written, and Mia Farrow’s delivery left much to be desired. The moment her voice started breaking into high pitch, as she was getting more neurotic, I wanted someone to strangle her a little.
This movie is all atmosphere with suspense and nothing else. It is nice to see something that attempts to approach the occult material with subtlety, but it is poorly acted and very slow. And that blunt ending is absolutely dreadful.