Full metal jacket.

IN CONTRAST TO the manga-addicted Japanese, Americans don't like comic books much. Sales have been sluggish since the collapse of the speculator-driven collectible bubble in the early 1990s. The fundamental flaw of comic books is that by using pictures to dispense with time-consuming verbal descriptions, they quickly chew through countless plot permutations, exhausting all but the most obsessive readers.

What Americans like instead, as the $100-million opening weekend for the entertaining "Iron Man" shows, are comic-book movies. Two hours is the right amount of time for the tragic death of the parents of the superhero, his dawning awareness of his powers for good and evil, a bruising fight with an older supervillain in the skies over a megalopolis, and an epilogue setting up the sequel.

Granted, Hollywood is scraping the bottom of the comic-book barrel with Iron Man, a name more famous as the title of the thudding heavy-metal classic by Black Sabbath. (Was the song inspired by the superhero? Nobody seems to know--you try getting a straight story out of an elderly English rock star about what he was thinking in 1970.) Yet Iron Man's obscurity didn't prove a marketing problem because, as Canadian journalist Colby Cosh has noted, "The public adores the familiar, even if all they know is that it should be familiar."

Iron Man was dreamed up in 1963 by Stan Lee as Marvel Comics's answer to DC's Batman. Like Bruce Wayne, Tony Stark lacked superpowers, but he made up for it by being a billionaire playboy inventor a la Howard Hughes. That was an era of engineer heroes, such as Hyman Rickover of the nuclear navy, Wernher von Braun of the space program, and Kelly Johnson of Lockheed's Skunk Works. In contrast, today's most celebrated tech tycoon is Apple's Steve Jobs, whose specialty is simplifying user interfaces (while the boring manufacturing is subcontracted off somewhere overseas).

Rather than fighting crime like Wayne, Stark's focus was foreign policy. While prototyping a new Stark Industries weapons system for our advisers in Vietnam, he was captured by "red guerilla tyrant" Wong Chu, who put him to work building a superweapon for some nefarious purpose. Stark, though, secretly banged together a robot exoskeleton (probably inspired by the mobile infantry power suits in Robert A. Heinlein's 1959 novel Starship Troopers) and smashed his way out.

The movie is transplanted to Afghanistan in 2008. The villain isn't the Taliban (there are a lot of Muslim potential ticket-buyers out there), but a freelance warlord who has assembled a multicultural gang of mercenaries from across the Eurasian steppe, from Hungary to Mongolia, to rebuild the empire of Genghis Khan. (How using Stark's high-tech weaponry to pillage one mud-brick village in the Hindu Kush gets him closer to world domination isn't explained.)

In most action movies, the bad guys' henchmen are suicidally devoted to the cause, even if they are just in it for money. In a clever touch of realism in this consistently enjoyable film, however, the hired goons are just bullies who flee in terror from what looks like a man wrapped in pick-up truck bumpers.

Soon the engineering genius is back in his workshop in his John Lautner-designed Iron Mansion in Malibu, building a more advanced suit to track down who is bootlegging his firm's weaponry. "Iron Man" is a refreshing throwback to the pre-virtual age when heroes forged tools out of metal, rather than just tapping on a computer keyboard. It's the most loving tribute to machinery since James Cameron vanished.

Casting the twice-imprisoned Robert Downey Jr. as the hero was a risk because the leading man in a $186 million production must be insurable, and his work ethic should provide a model for the crew. That's one reason Cameron made Arnold Schwarzenegger a huge star, even though he can barely speak English. Downey, in contrast, is blessed with the most nimble articulation of any American actor since James Woods. He could whip through "Hamlet" in three hours. Indeed, one of the more intriguing what-ifs of recent American theater history was the drug-cancelled 2001 production of "Hamlet," in which Downey was to be directed by his friend Mel Gibson.

Sober for half a decade, Downey remains the master of the throwaway line. Watch how lightly he tosses off his inevitable last line, "I am Iron Man," just before Black Sabbath's power chords clang over the credits.

Rated PG-13 for some intense sequences of sci-fi action and violence and brief suggestive content.