The best horror movie since Insidious and if only its Third Act could have maintained that level of creepiness, horror and originality, this would have easily been one of the best horror film in a long time.
Like Insidious, this movie focused its horror using old-school techniques of ratcheting up the tension, with the use of music and edits, and very, very minimal jump scares. The whole movie felt scary and the psychological terror that imbued in the audience was extremely effective.
Unfortunately, the final act fell apart. Not greatly, but still it felt flat compared to the excellent first two acts. It became rather generic and run-of-the-mill, and even then, because of the low budget, the run-of-the-mill-ness felt broken. Which was a real pity.
But nonetheless, the whole movie was definitely worth a watch for horror fans and even just the casual movie goer looking for a good scare.