I had been anticipating this one when it came out, and since then sort of forgot about it. I finally saw it with some hesitation, and... I liked it enough. The concept of appearing as a single-take is used for all it's worth. The cinematography is pretty brilliant, and really does make the film scary. There are some really great horror scenes here, scenes that amount to undeniable levels of terror. The other reason why the film is as unnerving as it is sometimes is because of Olsen. I haven't seen a performance this unbelievably scared as sh*t in a very long time, and Olsen squeezes the film's potential for all it's worth. Many times the reason you jump is because of Olsen's screams and terror. Not a very three-dimensional character, but a big reason the film works is because of how she delivers.
I was hoping I wouldn't hate the ending, but yeah, I kinda did. I got the big "twist" early on, as it's kinda obvious with how certain characters "communicate" with each other. Once the lead started seeing certain people and figures, I knew what had happened. That wasn't as much the problem as it was how they executed it. Very laughably idiotic, not to mention the dialogue was horrible and on-the-nose.
Very flawed ending and weak characters/dialogue, but otherwise a well- directed and impeccably photographed horror film with a brilliant central performance. This is another reason to keep looking out for Elizabeth Olsen.