At first glance, J. Robert Oppenheimer would not seem like an obvious choice for a sprawling, ambitious biopic.  As the father of the atomic bomb, his contributions to mankind were as monumental as they were controversial, but Dr. Oppenheimer (Cillian Murphy) was also enigmatic, eccentric, and prone to bouts of maddening passivity.  But in the hands of Christopher Nolan, Oppenheimer becomes a sweeping, audacious character study that fully embraces the deep melancholia of its subject.  For three hours, we see Robert Oppenheimer as a brilliant but tortured soul, destined to live in the billowing shadow of his own terrifying achievement.

You won’t need an expansive knowledge of WWII history to appreciate Oppenheimer, but Nolan probably assumes you’ve at least skimmed a few Wikipedia pages.  The story leaps around Oppenheimer’s life, from his days as a troubled young physicist to his postwar skewering during a Red Scare witch hunt.  Of course, the bulk of the film’s epic running time centers on Dr. Oppenheimer’s management of the Manhattan Project, the top-secret development of a nuclear fission bomb.

As WWII begins, intelligence reports suggest that not only have the Nazis already split the atom, but they’re racing to harness its energy in the form of a terrible weapon.  This sets off an arms race the Allies cannot afford to lose.  With that, General Leslie Groves (Matt Damon) tasks Oppenheimer to head up the project, deep in the New Mexico desert.

The doctor earns this position despite, or perhaps even because of several blemishes on his personal and professional resume:  Like many disaffected Americans, Oppenheimer attended a few communist meetings during the 20s and 30s.  He’s also a philanderer, conducting numerous affairs with a number of women.  This includes Jean Tatlock (Florence Pugh), a young physician and devout communist.  Add Oppenheimer’s aloof and haughty personality, and you get a team leader who’s paradoxically difficult to manage, but easy to silence.

Nolan intercuts the methodical progress of the Manhattan Project with flash-forwards to Oppenheimer’s disgrace as a communist sympathizer.  We meet Lewis Strauss (Robert Downey Jr.), a savvy bureaucrat who’s either a benefactor or mortal enemy, depending on which way the winds blow.  He plays an integral part in the hearings that aim to paint Oppenheimer as a shifty, leftist hypocrite.  Because they dredge up extramarital activities, they also embarrass Kitty (Emily Blunt), the doctor’s hard-drinking, long-suffering wife.

That’s just a quick skim of Oppenheimer’s plot.  This is a dense film.  Nolan chucks in subplots on subplots.  Smash cuts within flashbacks.  Flash-forwards that loop back.  Many Oscar-winning actors (Casey Affleck, Kenneth Branagh, Rami Malek) make glorified cameos.  Josh Hartnett shows up, only to disappear for long stretches.  This is the cinematic equivalent of a super-heavy meal; don’t be surprised if you have to undo your belt and slouch into a recliner after it’s over.

Predictably, Oppenheimer plays strongest when it focuses on the Bomb.  The Manhattan Project was one of the biggest secrets of the 20th Century, and Nolan whisks us behind the scenes.  These include extraordinary moments, such as when a member of Oppenheimer’s team dreams up the hydrogen bomb on a whim, or when a high-level meeting determines which Japanese cities to bomb.  (Kyoto is scratched from the list, as an undersecretary honeymooned there.  “It’s a beautiful city.”)

While the buildup in Los Alamos crackles with tension, the flash-forwards are, by design, more muted and cerebral.  In the aftermath of Hiroshima and Nagasaki, Oppenheimer grapples with waves of remorse and horror for his part in crafting the ultimate weapon of mass destruction.  He begs off building the H-bomb, much to the chagrin of hawkish Pentagon officials.  (Even Harry S. Truman is dismissive of Oppenheimer’s mounting anxiety:  “Don’t let that crybaby in here again.  Ever.”)  If the race to create the fission bomb builds up a strong buzz, then the flash-forwards are a long, haggard hangover.

Along that rise and fall, Murphy delivers a performances for the ages.  His Oppenheimer is a study in contrasts:  He’s likable, but unknowable.  Loving, but unfaithful.  Loyal, but dispassionate.  Murphy perfectly conveys the deep doubt of a man who can’t make sense of himself.  It’s tough to play enigmatic, but this is truly Oscar-level acting.

Naturally, Damon’s salty general is Oppenheimer’s emotional and spiritual counterpoint.  Terse and temperamental, Groves seems an expert in pissing people off and getting things done.  It’s unlikely the Manhattan Project would’ve produced timely results if Groves didn’t kick a few asses.  Damon brings real fire to this performance–also Oscar-level work.

Downey is another revelation, reigniting some of the promise that once heralded him as a chameleonic character actor.  His Strauss bears the poker skills of a master politician, manipulating and bullying until all the chips belong to him.  Strauss is either a bad man in service to the right people, or vice versa.  Few actors could tiptoe that moral line, but Downey makes it look easy.

Put all that together, and you have a showcase for world-class acting.  Much of this film’s emotional grip comes from its all-star cast.  Without their all-in commitment, Oppenheimer might’ve devolved into an overlong, overblown misfire.  Despite its clear success, some viewers might still find it to be too heavy and self-serious for its own good.

As for me, I’ll rank Oppenheimer as near-great.  Nolan takes a profoundly important individual and fashions a nuanced, emotionally-murky blockbuster around him.  To be sure, this is a difficult movie about a difficult man, and Nolan never shies away from its challenges.  In the end, Oppenheimer feels like a movie only he could make.

180 min.  R.  In theaters.