There are some genuinely chilling scenes. It does a good job at both: making the kids seem evil & possessed, and the governess just affected by the new setting, in the wrong. Deborah Kerr's performance is great.
The costuming is beautiful; and the superimposition of images in the dream sequence was so cool (for its time, at least) that it made me go 'now they are just flexing lol.'
It has that dense, literary quality to it. However, I didn't find the story and mystery that gripping. Her & the boy's arc does get weird leading to a few uncomfortable scenes.