It's entirely possible that sending the audience out feeling lousy was intentional

It's funny, it's tense, it features two great performances from two actors and the director expertly creates a web of odd tension where you actually don't know what is happening for the majority of the run time.

The plot isn't so bad, but the pace of storytelling is too slow which makes people bored. Certain moments are so obvious and unnecessary for the main plot. I would've fast-forwarded those moments if it was an online streaming. The ending looks like implying a sequel, not sure if this movie will get one

It is encouraging that the film ends so strongly.Otherwise, it wouldn't have been a particularly memorable film