Much of "Snowden" re-creates the scenes from Laura Poitras' documentary "Citizenfour," with Snowden (played by Joseph Gordon-Levitt) calmly divulging America's cybersecrets to a trio of reporters: Poitras (Melissa Leo), rebel freelancer Glenn Greenwald (Zachary Quinto) and grizzled Guardian writer Ewen MacAskill (Tom Wilkinson).
While Greenwald frets that The Guardian's editors will chicken out of Snowden's scoops, Poitras and MacAskill talk to Snowden about his motivations for becoming a whistleblower. This frames the movie's main narrative thread, following Snowden's career from an Army washout (he received a medical discharge after breaking a tibia in boot camp) to a star recruit in the CIA's cyberterrorism training center. At this point, Snowden is an idealistic conservative who can quote Ayn Rand and believes his talents can save the world from terrorists, a contrast to his left-leaning new girlfriend, Lindsey Mills (Shailene Woodley).
As he gets deeper into the intelligence world, spurred by his mentor (Rhys Ifans, deliciously duplicitous), Snowden starts finding the spy world morally dubious — not keeping the world safe but protecting American capitalism and smiting political dissent. He also learns from one cyberexpert (Ben Schnetzer) just how much the government can find out about innocent Americans through their computers and smartphones.
Stone plays this rude awakening like an espionage thriller, as Snowden tries to outwit spy-agency security to get the goods and deliver them to his reporter contacts. There's also a nice romantic strain, as Snowden's secrecy threatens to derail his relationship with Mills.
Gordon-Levitt's grounded performance, showing Snowden as preternaturally calm amid the computerized noise around him, keeps the movie from going off the rails. He's particularly good in those hotel scenes with Poitras, et al., though they still will feel repetitive to anyone who's seen "Citizenfour."
Only at the end, when the real Edward Snowden appears onscreen, does Stone's political pontificating overwhelm the very human story he's been telling. Up to then, "Snowden" worked effectively at dramatizing one man's moral dilemma without getting preachy.