Good concept, poorly executed.

Although it has its amusing moments, in eneral the plot does not convince.

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.

Let me be very fair here, this is not the best movie in my opinion. But, this movie is fun, it has purpose and is very enjoyable to watch.