Gotta watch it again
This film is a text book, bottle thriller. The tension and plot development mostly occurs at one location around a single room. Fantastic character definition and narrative movement. Also, excellent use of keeping the audience guessing as to what will happen next and how each character plays into the plot.
Beyond that it is also one of the most attainable features you could possibly watch as an upstart filmmaker. The writing and direction is spot on and the cinematography never gets pushed into impossible. Loved it.