The Witch is an extraordinary film, kind of unlike anything else out there. Sure, it has folk horror forebears, but it has a unique atmosphere that is all it's own.
Much of this is down to the now famous attention to detail, which I think does two things. Firstly it makes the world of the film more authentic and allows for suspension of disbelief. They actually built a replica of a 17th century farm out in the Canadian (standing in for New England) wilderness. The clothing is also as historically accurate that they could make it. The levels of research are phenomenal. It all seems really real and draws the viewer in properly.
Secondly, the dialogue is mostly taken from documents such as diaries, letters and court reports from the era in which the film is set. Again, this helps the authenticity but also creates a distancing effect. This could be a bad thing, but the amazing cast sell the hell out of it. The archaic verbiage is beautiful to listen to, but also adds to the feeling of weirdness the film does so well.
The atmosphere is also enhanced by how gorgeous the film looks (especially on Blu-Ray, yeah check ME out), but also how genuinely forbidding the woods and meadows seem. The family patriarch William tells his son Caleb that they will tame this wilderness, but the sinister surroundings seem to mock him even as he says it.
Then there's the score. The score is the reason I'm glad that I first saw the film in the cinema, because there are times when it is overwhelming. The first of these moments is when the family first enter the woods after being banished from town. It is the last time we see anyone who isn't the family or someone who isn't supernatural and malign. Their cart disappears into the dark trees and we cut to them camping in the woods on their first night. The strings and ghostly wails of the score build and build to an unholy, disorientating crescendo. For me it's the single most frightening moment in the film. The only other times the score does the same thing is at the end after everything has gone to shit (or has it) and when Caleb is seduced by the witch (the second most frightening moment in the film).
There's so much more. There's the puritanical religion of the family, so harsh it gets them kicked out of a community of Puritans. There's the allusions to actual folklore (something I know a tiny bit about so knew that freaky hare was bad news immediately). There's how the burgeoning sexuality of Caleb and oldest daughter Thomasin clashes with their religion and probably proves to be the downfall of the former. He is seduced by the witch after sneaking a glimpse down his sister's cleavage and ends up dying in mysterious, supernatural circumstances.
Then there's break out character Black Philip, the most terrifying goat in the history of cinema. By the end of the film we know he's not just a goat and that he may be Satan himself. Unlike most good modern horror films The Witch doesn't really traffic in ambiguity, but the one place it does is with the twins. The youngest members of the family after baby Sam disappears, it is fairly unclear whether they have been communicating with Black Philip or if they're just horrible little shits. They seem genuinely terrified when the crone turns up towards the end of film, but maybe they just realise they have taken things too far.
What else? There's the cuts to black, which seem to last an eternity and raise the tension. There's the eerie imagery (the apple, the witch taking flight, the raven, the posthumous visitations). There's the fact that the baby dies first.
Then there's the ending, where the Devil turns up/has been there all along and offers Thomasin a way out. There's enough to Anya Taylor-Joy's beautiful performance that suggests she may have taken deal even if everyone else wasn't dead, that family a piety was starting to suffocate her already. When that score rises again at the end and Thomasin rises with it, it sounds more ecstatic than harrowing.