The success of Iron Man is due less to the titular man in the metal suit than to his plainclothes alter ego, Tony Stark. Sure, there are plenty of action scenes to set the superhero mood: high g-force jet fights, raucous explosions and a multiple-villain takedown straight out of Terminator 2. The computer-generated effects even have an admirable heft to them, giving weight and presence to the laser blasts and aerial displays that can feel cartoonish in bad hands.

But where the movie really succeeds is in the acting of Robert Downey Jr., who exudes the insouciance and charmful arrogance that should be demanded of any millionaire playboy. His Tony Stark “works hard and plays hard,” to use a cliché. The head of a weapons-manufacturing firm, he’s consistently late and chronically soused. All-day immersions into genius engineering give way to all-night sessions of lovemaking. His private jet has a stripper pole; it’s probably also the fastest thing on the planet.

Downey’s performance reflects a man of gifts and privilege with a non-stop need for stimulation. Tony Stark seems to be living up to a thirteen-year-old’s image of a billionaire’s lifestyle, but a tinge of self awareness and a consistent sense of humor keep the whole thing grounded. Excellent supporting performances from Terrence Howard (college buddy/military man James Rhodes), Gwyneth Paltrow (right-hand assistant Pepper Potts) and Jeff Bridges (menacing mentor Obidiah Stane) lend the film a human feel that balances its high-flying action.

The movie even takes steps toward engaging the genre’s inherent contradiction—people pummeling others in the name of stopping violence—as Stark becomes disenchanted with his business after seeing arms he’s manufactured used by the wrong people. True, it doesn’t go very far in exploring the inherent limitations of Iron Man’s forceful approach (nor does it engage the difficulty of determining “the wrong people”), but hey, that’s what a sequel is for.