The modern superhero trilogy has a very specific arc. There's the origin story, in which an everyman stumbles into great power. In round two, the world turns on said hero as he faces greater threats. And in round three, our hero delves into an existential crisis, forced to grapple with his duality. 

The Iron Man trilogy is no exception. But it's an outstanding example of how familiar territory can be explored so compellingly. In 2008, Marvel took a big gamble with the story of Tony Stark. The self-proclaimed genius, billionaire, playboy philanthropist wasn't just an untested cinematic commodity who was essentially on the superhero B-list. He was also poised to be a protagonist with whom no viewer could identify: egomaniacal, self-serving, alcoholic and warmongering. Marvel was asking a lot of audiences to embrace the man and his redemption. 

But in casting then-struggling Robert Downey Jr. as the man in the can, the studio managed the impossible. Downey's Stark is the very definition of charismatic. Unlike another billionaire with daddy issues in an armored suit protecting the world, Stark uses his wealth to womanize and globetrot. He flaunts his riches and his heroic alter ego with a series of nervous tics and rapid-fire quips. He's the anti-Batman. 

As a result, the first Iron Man film emerged as a top-tier superhero yarn that emphasized something too often forgotten by its brethren: Comic-book movies are supposed to be fun.

After a slight misfire with his second outing and a tremendous role in The Avengers, Downey is back to headlining. Given the setup, the flick could have been a total downer. This is, after all, the phase of the story where things get dark, with Stark stripped of his suit by a murderous terrorist with shades of bin Laden known as the Mandarin (Ben Kingsley), who commands an army of genetically modified soldiers who specialize in mass murder via bombing. Plagued with crippling anxiety in the aftermath of The Avengers and struggling to maintain his relationship with Pepper Potts (Gwyneth Paltrow), Stark is a hot mess. None of these elements lends itself well to a crackling summer popcorn flick.

Yet Iron Man 3 is perhaps the most giddily enjoyable superhero flick of the Marvel lot, a hysterically funny, fast-paced character study that revels in its explosions as much as it does its whip-smart dialogue. From the opening flashback to the prolonged final melee, nearly every moment bursts with energy, smarts, rascally charm and surprises. 

In reuniting Downey with Kiss Kiss Bang Bang director Shane Black, Marvel has managed yet another home run in a series of blockbuster gambits. In Black—the man who invented the banter-driven buddy-cop genre with Lethal Weapon—Marvel has finally found a writer who can convey Stark's gift for fast talk and self-deprecating barbs. He's populated his film with loquacious henchmen, slapstick sight gags and enough putdowns to fuel 1,000 celebrity roasts. And in keeping Stark out of his armor for much of the film, Black has crafted a superhero film that harks back to the golden years of summer action: As Stark and Rhodey (a returning Don Cheadle) infiltrate the Mandarin's compound armed with their wits and fists, the two actors are allowed to let their mouths run rampant. 

That's to say nothing of Guy Pearce, as villainous inventor Aldrich Killian, who turns in a performance of such slimy charm that he nearly matches Downey beat for beat, or Kingsley, who spouts rhetoric and malice with scenery-chewing relish. Iron Man 3 isn't just a fine superhero film. It isn't just a fine action flick, either. It's a film that embraces a mold before completely breaking it with left-field twists and turns that keep the viewer engaged and chuckling with alarming frequency. Never before has a film about a hero's existential dilemma and descent into darkness been this much fun. And never has a movie about a dude in a robot suit blowing up shit had this much heart. 

Critic's Grade: A-

SEE IT: Iron Man 3 is rated PG-13. It opens Friday at Cedar Hills, Eastport, Clackamas, CineMagic, Lloyd Center, Bridgeport, Division, Evergreen Parkway, Lloyd Mall, Pioneer Place, Movies on TV, Roseway, St. Johns Twin, Hilltop, Sherwood, Tigard, Wilsonville.