OMG! I went to a preview screening of this (out middle of Jan I think) and I was captivated. The film stayed with me for days afterwards and I just couldn't stop thinking about it. I always think when this happens it's a good indicator that the film is really great.
The acting by Brie Larson and Jacob Tremblay just blew me away. It's a harrowing, grim story and they bring it to life in a way that makes you feel you are there with them experiencing every second. This makes it sound unwatchable, it's not, it's a work of art and the best movie I've seen for a long while.