(CNN) -- You might attribute it to 9/11, or simply blame director Joel Schumacher, whose camp take on "Batman" derailed that franchise for several years. But, lately, Hollywood superhero movies have taken themselves awfully seriously.
Robert Downey Jr. plays Tony Stark, a billionaire who remakes himself into "Iron Man."
Ang Lee, Bryan Singer and Christopher Nolan have produced solemn, almost morbid versions of the Hulk, Superman and Batman, respectively. Even Sam Raimi succumbed to this gravity in the "Spider-Man" trilogy.
Enter Robert Downey Jr., riding to the rescue, a glass of Scotch in his hand and a sardonic smile on his lips. As everyone knows, Downey is not the hero type. Not in his public persona and not on screen either, where his dissipated narcissism has been most often effective in supporting roles ("Zodiac," "A Scanner Darkly," "Wonder Boys").
Downey is one of those actors who likes to doodle in the margins, to ad-lib and fool around, instincts that give Jon Favreau's "Iron Man" movie an immediate fillip. The star's bad-boy past becomes part and parcel of the character's redemption drama: This is where he shows his true mettle.
One of the lesser-known Marvel heroes, Iron Man is basically Batman in a shiny new suit and a more global perspective. Like Bruce Wayne, Tony Stark is a wealthy industrialist, a weapons manufacturer with the means and know-how to create his own impregnable armor (Stan Lee allegedly based him on Howard Hughes). Iron Man made his debut in 1963, when he was captured by the Viet Cong and put to work.
Forty-five years later the theater of war has shifted to Afghanistan, but the same mechanics are in play. Stark is demonstrating his latest smart bomb -- part of the "Freedom" line -- when he falls into the hands of a murderous warlord who turns out to have a well-stocked arsenal of Stark hardware. The warlord then demands his own, homemade weapon of mass destruction.
Badly wounded, Stark feigns compliance, but actually hammers out the prototype for a bulletproof jet-suit that he uses to escape.
In the original comics, Stark's brush with mortality only made him angry; he took the war to the Commies. Favreau's reconstructed Iron Man is still a human gun, but he's no longer gung-ho, exactly. He's more of an aggressive pacifist.
Back in the USA, he announces he's a changed man, embraces nonviolence and joins a Buddhist commune. OK, I'm kidding, but not by much: He announces that Stark Industries is quitting the arms trade. As the stock plummets, he quietly holes up in his modernist Malibu home to perfect his one-man missile defense system.
True to type, Downey has a ball as the cavalier playboy in the early scenes. This Tony Stark is so much fun to be around we're almost sorry to see his transformation take place. Or we would be, if not for Downey's deliciously deft physical performance, which insists that the melding of man and machine is no walk in the park.
However, his business partner, Obadiah Stane (a splendidly bald, bearded Jeff Bridges), is unhappy about the change.
It's not difficult to guess where this is heading -- Marvel stories are all permutations on a handful of stock scenarios -- but Favreau doesn't blow it up any more than he has to. In "Elf" and "Zathura" he showed he could integrate special effects and carry the story, but like Downey, he's almost always looking for a comic spin.
A scene in which Tony invites his assistant, Pepper Potts (an appealingly valiant Gwyneth Paltrow), to reach into the hole in his chest and fix his battery is a cheeky cocktail of trust, disgust, love, sex, fear and courage (it's also a key plant for subsequent developments), but above all it plays funny. When a movie is firing on all those cylinders, you know it's a winner.
The character stuff is so light on its feet that the action scenes seem flat in comparison -- the effects are first-rate, but they're nothing we haven't seen before, and the climactic showdown is a bit heavy-handed (if satisfyingly crunchy).
Even so, "Iron Man" is a supremely confident, well-tooled entertainment. It's bound to be the early pace-maker for the oncoming glut of summer blockbusters.