If I can give one recommendation before watching this film, it's this; don't watch it late at night when people are trying to sleep. It goes from practically silent to waking-the-whole-street loud without a moment's notice. Your thumb will never leave the volume controls. You can thank me later.
Volume issues aside, The Witch was brilliant. It wasn't as frightening as I was led to believe, more unsettling than scary. But it when it unsettles it moves the ground from under you. The slow pace works perfectly. A friend said every shot looks like a painting and he's right. The lack of movement played well into the story, representing the lack of control these characters have, their devotion to their religion crippling them and ultimately leading to their downfall.
The horror is mostly unseen, letting the imagination run wild. Amazing performances from the entire cast, especially the creepy twins. What is it with twins in horror films? Are the Grady twins from The Shining distant relatives? I couldn't watch the baby bit.
All in all, The Witch is another great example of modern horror injecting new life into the genre. It ignores the conventions and creates an identity unique to itself.