Robert Downey Jr., left, as Tony Stark in “Iron Man 2.”  By A. O. SCOTT NY TIMES

“Iron Man 2,” the first superhero sequel of the summer, fulfills the basic requirements of the genre, which can be summed up as more of the same, with emphasis on more. Having introduced its physically and intellectually gifted, emotionally tormented protagonist in both his regular and alter egos, a comic book franchise will typically set out, in the second installment, in search of new villains, bigger suits, brighter gadgets and tendrils of plot that can blossom in subsequent sequels.

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Industrial Light & Magic/Marvel

A scene from “Iron Man 2.”

 

Industrial Light & Magic/Marvel

Mr. Downey Jr. with Scarlett Johansson.

But sometimes — for instance in the recent Spider-Man, X-Men and Batman cycles — the second time is a charm, as filmmakers and actors use the reasonable certainty of financial success to take chances and explore odd corners of their archetypal, juvenile stories. “Iron Man 2,” directed by Jon Favreau from a screenplay by Justin Theroux, doesn’t achieve the emotional complexity of“Spider-Man 2” or the operatic grandeur of “The Dark Knight,” but it does try something a little bit new and perhaps, given the solemnity that has overtaken so much comic-book-based filmed entertainment, a little bit risky. It’s funny.

Mr. Favreau and Mr. Theroux are both accomplished actors — in “Iron Man 2” Mr. Favreau again plays Iron Man’s nebbishy gopher — and they have in effect turned this movie over to its game and talented cast. It’s not that the action sequences are badly executed; they just aren’t very interesting. The suits and explosions and C.G.I. flight simulations may have cost a lot of money, but more imagination has been invested in the film’s sleek and shiny look and, above all, in its jittery, loquacious and eccentric population of geniuses, frauds, playboys and bad guys.

At the head of this crew — and playfully keeping everyone guessing as to just which of those categories he fits into — is Robert Downey Jr.’s Tony Stark. Stark has the identity issues and daddy problems that come with the superhero territory, but self-pity is as alien to him as false modesty. An apostle of pleasure, progress and the free market, he is the kind of devil-may-care, lady-killing capitalist demigod that just about every hedge-fund cowboy and high-tech guru of the past 10 years has dreamed of being. And he cares too: about world peace and race cars and scientific innovation, among other things.

Mr. Downey, his restless features keeping Stark’s lounge-lizard facial hair in a state of perpetual animation, has a way of turning action-hero duty into a form of intellectual comedy. As fast as his body and mouth might move, his brain is even quicker. He has the rare and marvelous capacity to surprise himself, which is one reason, even in a noisy dud like “Sherlock Holmes,” you can’t stop watching him.

But though Tony is a narcissist — he admits as much when a psychological profile tells him so — Mr. Downey is happy to share attention with any actor possessing the nerve and verve to try and keep up with him.

Gwyneth Paltrow, as Pepper Potts, Stark’s right-hand woman, informal nanny and unacknowledged love interest, handles the rematch with even more exasperated aplomb than the first time out. Every encounter between these two is a flurry of interruptions, miscommunications, false starts and premature conclusions. At a time when romantic comedy has abandoned its tradition of witty dialogue in favor of either simpering or crudity, apparently it falls to a comic book spectacle to keep the screwball tradition alive.

In addition to his Girl Friday, Stark also has a nemesis, a sidekick (Don Cheadle, replacingTerrence Howard) and a designated heel. The heel is a rival armaments mogul named Justin Hammer, played with a sublime mixture of pomposity and cluelessness by Sam Rockwell. Hammer is Daffy Duck to Stark’s Bugs Bunny, forever trying to outdo his competitor and discovering new registers of pique and humiliation every time he falls short.

Which would make Mickey Rourke’s Ivan Vanko — what, exactly? The Tasmanian Devil? Yosemite Sam? There is something of a physical resemblance to both, but Mr. Rourke composes a fugue of malevolence in his own demented key. Vanko, like Stark the son of a military scientist, is what his lucky enemy might have been if the cold war had gone the other way. His body covered with Russian prison tattoos, his face a fleshy mask of bitter pride, Mr. Rourke takes possession of the movie every time he shows up. In his first few seconds on screen he speaks Russian and plies a cockatoo with vodka. Later he dons a high-tech supervillain suit complete with fiber-optic whips and a breastplate like Iron Man’s, but none of that can match the silky menace of his line readings.

There are, I suppose, viewers who will regard the comic filigree of “Iron Man 2” — and I haven’t even mentioned Clark Gregg’s deadpan secret agent or Garry Shandling’s bloated senator — as diverting or distracting filler deposited between action sequences and plot revelations. I take the opposite view. A bunch of guys in metal suits slugging it out in a park in Queens? I can probably find that on pay-per-view or even YouTube. And the plot of “Iron Man 2” is frankly a bit of a hash, as Stark’s two-front conflict with Hammer and Vanko competes with exposition that will only pay off (meagerly, I suspect) in later sequels.

Such preparation is one reason that Scarlett Johansson and Samuel L. Jackson show up here, though there are of course others. Mr. Jackson looks good in an eye patch, as Ms. Johansson does in tight skirts and tighter body suits. So you might say that the movie has something for everyone, which is fine but also, in the end, not quite enough. You’re left wanting more, but not quite the “more” “Iron Man 2” works so hard to supply.

“Iron Man 2” is rated PG-13. It has swearing, mayhem, discreet bloodshed and sexual innuendo.