Let's be realistic.

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 movie's neither hopeful in contrived ways, nor hopeless in different contrived ways. Somehow it manages to be wonderful

It is neither dumb nor smart enough to be fun, and spends way too much time with its boring human characters.