Lack of good storyline.

Simple and well acted, it has tension enough to knot the stomach.

The film makes a home in your brain and the only cure is to see it again.

Just intense enough to provide a much-needed diversion, just lightweight enough to make you forget about it soon after it’s over. It’s not exactly “good,” per se, but it does what it sets out to do in terms of putting us on edge, which makes it … successful?