Lack of good storyline.

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.

I think this is a new genre that they're all sort of working their way through it and haven't got all the kinks worked out yet but it's a genre that works for me.

Yes, absolutely, there is fun to be had, as well as many, many things to go boom, all amid an atmospheric urban jungle.