The movie is outstanding in the premise, cinematography, performances and visual choices. It is a “must watch” film. Beyond that, the movies struggles with keeping the plot-line engaging and intriguing. When the decision is made to keep only three characters in entire film, it becomes imperative to have a solid storyline that keeps the pace. This is where the movie falters. The edit could have been tighter. Had the film wrapped up in 1hour and 20 or 30 minutes, it would have been more thrilling. Since the movie had an uncomfortable and unconvincing climax, a shorter length would served well.
I do wonder what the same film would have looked like in a saturated colour or in a mix of B&W and colour. Perhaps the film makers could re-edit and re-release with experimentation with colour and length.