IRON MAN-2

He may be out of the closet as a superhero and cheered around the world as a peacekeeper, but in Iron Man 2, former weapons mogul Tony Stark (Robert Downey Jr.) can still be a cocky SOB. The man with a battery where his heart ought to be is restless, driven, glib, grandiose — which is to say, the billionaire industrialist still exhibits all the self-absorbed, antiheroic qualities with which Downey first delighted us in the role two years ago. So if this sequel doesn't glow with the same charm as the original, and if Iron Man's face-offs against evil lack edge, the diminished satisfaction has less to do with the quality of the star's trademark catch-me-if-you-can energy than it does with a performance anxiety that now pervades the whole shebang.

Are returning director Jon Favreau and the Marvel Studios producing team buckling under pressure to give the people more of what they think the people want, and make it bigger, too? That's the only reason I can think of for the time and money devoted to loud, long, escalating battle scenes, waged among inconsequential war machines (there's nothing duller) that are themselves merely the products of CG artists — undifferentiated action sequences that stall long stretches of the story and threaten to stomp out the quotient of fun. Which is an odd choice, since people who loved the original are exactly the people who don't want clang for clang's sake: We want zingy repartee, we want characters, we want attitude to spice up the further adventures of a superhero still getting used to the demands and perks of the job, and drinking too much under stress. We want what Downey had in mind when he pushed for Justin Theroux to write the screenplay: quick-thinking wit from the hip writer-actor who co-wrote Tropic Thunder.

Naturally, we also want a few juicy bad guys. Here, we're given a choice of villainous types. Mickey Rourke goes for Slavic-psycho stylings as a grimy Russki creep named Ivan Vanko who's been nursing a long-festering complaint against Stark's late dad (John Slattery, in a nice touch, is seen in '60s-style film-reel flashback living the Mad Men life). In a contrasting star turn of virtuoso smarm, enhanced by the telling detail of self-tanning dye stuck to his palms, Sam Rockwell struts and preens as arms manufacturer Justin Hammer, always ready to cut a corner to fill a military contract.

For a change, we're given a choice of pertinent dames, too, as Stark interacts with two very different female employees. His loyal, spunky former assistant, Pepper Potts (reprised by radiant, ponytailed Gwyneth Paltrow, bright as a penny), has been promoted to CEO of his company, allowing the boss to go all hound-dog around her curvy, purring (and, as it turns out, secretly busy) replacement, Natasha, played in full come-hither mode by Scarlett Johansson. (Natasha, you may have heard, reveals her true identity soon enough, and does a passable superheroine martial-arts crouch in a skintight bodysuit.)

The Iron Man 2 story expands from a lot to a whole lot. Along the way, Stark becomes obsessed with reviving his father's plans for a showcase for the humanitarian uses of cutting-edge technology. Stark broods (as only a Downey character can) over the progressive corrosion of his substitute heart. And there's a dispensable detour involving Stark's military buddy, Rhodey (played by Don Cheadle, replacing Terrence Howard in a thankless role).

With all that heavy payload, Iron Man 2 begins to burst at its own galvanized seams as the Marvel instinct for faceless warfare among comic-book characters bangs up against the Downey-Favreau-Theroux instinct for goofitude. (Qualifying as goofy, comedian Garry Shandling plays a U.S. senator, Bill O'Reilly plays himself, and at one point Iron Man, resting curled within the curve of a famous Southern California food-sculpture landmark, is told, ''Sir, I'm going to have to ask you to exit the doughnut.'') Downey's head and heart are in the right place, but the movie is more in pieces than whole, and more about iron than about men.