Joseph Gordon-Levitt stars as Edward Snowden in Oliver Stone’s new film, starting with a brief military career after the terrorist attacks of Sept. 11, 2001. (Open Road Films)

At first glance, viewers may think they know what they’re going to get with “Snowden,” a movie about national security whistleblower Edward Snowden directed by Oliver Stone. One of America’s most polarizing filmmakers turning his sights on one of America’s most polarizing figures? Let the bomb-throwing begin.

Not so fast. “Snowden,” which Stone and co-writer Kieran Fitzgerald adapted from two books about the real-life figure, turns out to be a relatively straightforward, sober-minded, even somewhat restrained film, a far more classical and conventional piece of filmmaking than the kaleidoscopic, conspiracy-minded “JFK” or the Shakespearean gloom of “Nixon.” That stylistic choice subtracts nothing by way of urgency or timeliness: “Snowden” is a superbly crafted, engrossing film that, while making no bones about admiring the central character’s actions and motivations, doesn’t go to visual or psychological extremes to make its case.

That case, in brief, is that Snowden is an idealist and a patriot, a reluctant activist whose disillusionment with the government he worked for finally overtook his reflexive loyalty. “Snowden” is unlikely to sway those who already consider Edward Snowden a traitor, an opportunist or a useful pawn in a new, Putin-era Cold War. (He still lives in Russia after having his U.S. passport revoked at the Moscow airport in 2013.) But the film reminds viewers of the issues at stake — having to do with security, civil liberties and democratic consent — which feel more urgently necessary than wild-eyed or alarmist, especially as we face a crucial political transition. American citizens may feel that trading their privacy for safety is worth it right now, but in the wrong hands, the capabilities of our modern-day security state might be paving the way for what one character describes as “turnkey tyranny.”

Oliver Stone's newest film follows the story of Edward Snowden (Joseph Gordon-Levitt), who leaked classified information from the National Security Agency in 2013. (Open Road Films)

Played in an extraordinarily nuanced performance by Joseph Gordon-Levitt — who has mastered Snowden’s flat, affectless way of speaking — the title character starts out as a bright if enigmatic young man who seeks to join the U.S. Army Special Forces after the attacks of Sept. 11, 2001; the film follows his early days in the military (cut short after a debilitating training injury) and into the world of intelligence, where he worked as both a staffer and a contractor, first for the CIA, then the NSA. Framed by his fateful 2013 meeting in Hong Kong with the journalist Glenn Greenwald (Zachary Quinto) and the documentary filmmaker Laura Poitras (Melissa Leo), to whom he initially leaked his information, “Snowden” flashes back in time, methodically tracing his dawning awareness of mass surveillance the U.S. government was either practicing or poised to practice — and not just on terrorists and hostile regimes, but on allies and everyday citizens. (Not surprisingly, “Snowden” spends less time on how Snowden’s revelations might have compromised sensitive military and security operations.)

As Snowden’s unease grows, so do problems with his girlfriend, Lindsay Mills, played by Shailene Woodley with earthy warmth and delicacy. The movie balances the political transformation of Snowden — who as a young man considered his biggest influences to be mythologist Joseph Campbell, “Star Wars” and Ayn Rand — with brief tutorials on the Fourth Amendment, the Foreign Intelligence Surveillance Court and the Nuremberg principles, as well as domestic scenes of Edward and Lindsay clearly designed to show what he gave up when he walked out of an Oahu cybersecurity facility with a computer chip containing hundreds of thousands of classified NSA files.

“Snowden” subtly raises the possibility that some of Snowden’s colleagues in Hawaii might have had an inkling of what he was up to. Other than that tantalizing what-if, the film doesn’t reveal much that wasn’t covered in Poitras’s Academy Award-winning 2014 documentary “Citizenfour.” If anything, seen alongside that film, as well as Alex Gibney’s recent documentary “Zero Days,” about the most shadowy aspects of cyberwarfare, “Snowden” enhances their messages, providing texture, context and humanity to what could otherwise be dry policy arguments.

Crisply photographed by Anthony Dod Mantle and adroitly edited by Alex Marquez and Lee Percy, “Snowden” winds up being not just a provocative viewing experience but a powerful one, thanks to a piece of editing at the end of the film that is breathtaking in its grace and dexterity. Regardless of how they feel about the main character, most viewers are likely to leave the theater reminded of Stone’s instinctive brilliance as a filmmaker — his grasp of visual language not just to tell a story but to expose its essential emotional core. “Snowden” is worth watching for the ideas and arguments it inspires, and for the layers of a still-mysterious character it reveals. But, most gratifying for movie fans, it also happens to mark a stirring return to form for one of our most gifted directors.

R. At area theaters. Contains profanity and some sexuality and nudity. 134 minutes.