Directed by Adam Wingard (director of You're Next & The Guest), it was made in secret. A teaser trailer was released months ago with title listed as "The Woods". There was rumours that it could be a Blair Witch Project sequel, but the studio & director were adamant (as they would be if they were trying to keep a secret) that it was a brand new original idea.
It screened at ComicCon back in August & it wasn't till the title came up that it was revealed as a Blair Witch Project sequel. Obviously ignores the not-canon Blair Witch: Book of Shadows & just picks up the story from the original, 20 years later (or, well, 22 I suppose, seeing as the original took place in 1994.)
All the reviews I've read say it's anywhere from just tolerable to downright awful. It has a 36% rating on Rotten Tomatoes, and the audience ratings are almost as low. Don't know how some people here have the impression that the reviews are generally favorable for it.