After Laura Poitras received encrypted emails from someone with information on the government's massive covert-surveillance programs, she and reporter Glenn Greenwald flew to Hong Kong to meet the sender, who turned out to be Edward Snowden.

The documentary of the year may also be its most hair-raising thriller. Part of Laura Poitras’s Citizenfour’s thrill is that it allows the viewer to experience, first-hand, history being made, as National Security Agency whistle-blower Edward Snowden, hiding in a Hong Kong hotel in the summer of 2013, exposes how the U.S. government used an unprecedented global surveillance program of phone calls, e-mails, debit transactions and Web searches in the trillions. For those who think the Snowden revelations are already old news, the movie offers extensive fresh justifications for paranoia, including more evidence of unbounded government surveillance and a final kicker promising bigger revelations to come.