This movie was based on a popular but second-rate novel by Anya Seton.
Seton set a Gothic melodrama, obviously inspired by 'Jane Eyre' and 'Rebecca', within a historically accurate account of the Anti-Rent Wars that took place in upstate New York during the 1800s. The result is a mess. The historical information is boring (it reads like something copied from an encyclopedia) and the melodrama is equally boring (it reads like something copied from a 'Cliff's Notes' version of 'Jane Eyre'or 'Rebecca').
But there are some good things in the novel, just as there are some good things in the movie. Unfortunately they are not the same things.
The best thing in Seton's novel is its Byronic antihero, Nicholas Van Ryn. Nicholas is a blond and handsome Greek god, and Miranda, the heroine, naturally falls in love with him the moment she sees him. Unfortunately her hero is tied to a selfish and whining invalid wife.
As in 'Jane Eyre' and 'Rebecca', the death of the wife frees the hero and heroine to marry. But unlike 'Jane Eyre' and 'Rebecca', Dragonwyck's hero is also its villain.
When Miranda discovers that Nicholas murdered his first wife, she runs away. Nicholas pursues her, presumably to prevent her from revealing his secret by killing her, just as he killed his first wife. But when their steamboat catches fire, Nicholas rescues Miranda, and dies while rescuing other passengers. He is a complex character, both villain and hero.
The movie cuts most of the historical background, and what little remains of it is confusing. But the worst change is the movie's Nicholas Van Ryn. As played by the saturnine Vincent Price, he is obviously a villain, and Gene Tierney's Miranda seems stupid for not recognizing him as a villain the moment she sees him.
There are some good things in the movie as well. The lush music and elaborate period decor are enjoyable, and Tierney does her best with a plot that gets more and more ridiculous the further it deviates from the novel (instead of dying bravely rescuing passengers from a burning steamboat, Price's Nicholas goes mad and is hunted down, like Frankenstein's monster, by irate villagers).
This movie is worth a look, but don't expect too much.