Just watched Resolution and then The Endless, and enjoyed them quite a bit. Funny thing is, Resolution was more attention-grabbing, but the ending fell a little flat for me. However, while watching The Endless, it basically gave me the "closure" I needed for Resolution! If you haven't watched them that statement won't make much sense, but if you do get around to watching them, make sure you watch them both, and in that order.
They were definitely movies that you have to be in the right mindset for, and while I enjoyed them quite a bit overall, they weren't anywhere near my favorite movies ever like a lot of critics seem to say. I never felt bored, but it is also hard for me to recommend to the dumb people I work with, for instance. They might not even catch on to what is going on despite watching both movies fully. So I definitely give them a thumbs high, but feel the need to temper it by saying that they are pretty heavy movies, but pretty light on details, particularly Resolution.