A lot of people won't like it, but its more traditional slow building suspenseful horror. We lapped it up and thought it was time well spend and a lot of food for thought. People analyze this on several levels.
Watched it twice and so much going on that the rewatch was a different take. Won't give anything away except for that several interpretations of the film exist. A thinking horror film. This is a good introduction to suspense horror. Nice that its a Hammer film.
Mind you I like films like The Witch and Lighthouse so take my recommendations with a grain of salt.
But with horror specifically, as a genre, I like to go back in time and assess how this would have impacted a younger audience. This one is slow haunting, one that you don't forget, years later will be remembered. Wife got a good dose of nightmares from this one. Its that kind of movie that just creeps into your spine. Deliciously, you don't even realize it immediately.