I agree. In the genre we call Gothic fiction, it's absolutely brilliant. Concise, atmospheric, just enough but never too much horror. I'm sure that a movie would be just awful.
I have not read "The Haunting of Hill House."
You’ll devour “Hill House.” It’s a marvel of suspense, atmosphere, and her uncanny way of drawing characters like a pure artist. It’s a must, and will leave you shaken.
I have often described "We Have Always Lived..." as unfilmable. What makes it so frightening is not the plot, but the first-person narration-- reading the book like being in telepathic contact with a lunatic.
I have not read "The Haunting of Hill House."
Then buy it or download it now. If you like Jackson at all, you need to read "Haunting." The first paragraph will haunt your sleep.