There haven't really been any horror films that have knocked my socks off this year, but I think I would have declared "Citizenfour" to be the most terrifying movie of the year either way.

There haven’t really been any horror films that have knocked my socks off this year, but I think I would have declared “Citizenfour” to be the most terrifying movie of the year either way.

Sometimes the stars have to align for a great documentary, a combination of fortuitous access to events and the talent to capture them. Documentarian Laura Poitras was in the right place when she started receiving anonymous encrypted emails from someone called “Citizenfour” who claimed to have proof of wide-reaching NSA surveillance that cast a blanket over much of the world.

Citizenfour was, of course, Edward Snowden. The historic importance of his whistleblowing is still being determined — in part by how much citizens pay attention to what’s going on in this movie — but the moment in time that’s captured in this documentary is pretty amazing.

“Citizenfour” succeeds as an informative “cause” movie about the fact that many of us have already ceded every possibility of privacy in the digital age. In explaining why he came forward, Snowden says, “I remember what the internet was like before it was being watched.”

It’s an eye-opening film, one that should make you angry, but it’s also a tense real-life thriller, as Poitras and journalist Glenn Greenwald meet Snowden in a Hong Kong hotel before his identity was revealed.

Snowden rightly predicts the media’s tendency to “focus on personalities,” and his has already come under scrutiny, but “Citizenfour” is both one of the most important documentaries of the year and one of the most enthralling.