Let's be realistic.

This is one of the few movies I've ever seen where the whole audience broke into spontaneous, loud applause a third of the way in.

While it doesn't offer any answers, it both thrills and makes you think.

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.