I really liked it.
As an artist, the movie sort of gripped me by the shoulders. I was much more fascinated by the performance and shot composition of the movie rather than the plot. There were a few plot holes here and there, but I don't think the plot was the point of the movie.
The point of the movie, to me, was the raw emotion of what you were watching. You could tell Dafoe's character had been put through a state of extreme psychosis due to the extreme heat that had initially overcome the penthouse and the lack of water and food. I saw myself project onto Nemo, and be able to empathize with the pure desperation he felt while trying to figure out a way to escape. The movie's focus is on the raw emotion of Dafoe's performance. A means of seeking a way out of the penthouse was just providing the movie with an end goal to finish the film.
The film is actually quite subversive in that aspect. Many films have heavy focus on plot and logic, rather than pure, raw emotion. The film is not meant to be grounded in reality. Dafoe's character can barely keep himself sane anyway, and the writing seems to emphasize that. No movie is perfect, and I think the flawed pace of this film helps to elevate the core message.
This movie definitely isn't for those who have an objective approach in interpreting the film, or those with a low patience. Give it a watch if you're willing to sit through a lot of uncomfortable silence. I think it's worth it, personally.