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.

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

A great movie, one of the best of this year. There was a bit of confusion at one point in the plot, but nothing serious.