Iron Man, (12A)

Heavy metal hero

For some actors, the starting point for a performance is the shoes or the false nose; for Robert Downey Jr, it seems to be the goatee – just how straggly will it be this time? The more dishevelled, as a rule, the more tormented and unreliable the character. The question has particular importance in the case of Tony Stark, the billionaire weapons designer who becomes the armoured superhero Iron Man.

As devotees of the original comic will know, Stark always wore a Clark Gable-style pencil moustache; but while back in the 1960s, when the character first appeared, that might have suggested suave sophistication, these days it would signify affectation and perhaps slightly outré sexual tastes (think Willem Dafoe's Bobby Peru in Wild At Heart). In the event, Downey begins with something quite tightly groomed – a little bit Charles II, the Merry Monarch – but my impression was that it thickens slightly over the course of the film, growing in concert with Stark's moral stature.

Maybe that's fanciful (although in the context of a film about a man in a flying metal suit with a generator implanted in his chest to stop his heart bursting, "fanciful" is hardly a useful term). But it is true that Iron Man is by the standard of superhero yarns unusually, even uniquely, thoughtful, witty and three-dimensional – a popcorn movie that has some of the satisfactions of a proper three-course meal.

Much of this richness comes from Downey, who gives a supremely funny, intelligent performance as Tony Stark, a man insulated from nearly all life's strains and disasters by vast amounts of money and brains – charming but a little disconnected, his conversations limited to exchanges of snappy one-liners, from which he always comes out best. He doesn't have scruples about arms-dealing, trotting out the line that strength is the best guarantee of security; he doesn't have a girlfriend, either, just a lot of one-night stands: like the Tin Man, he lacks a heart.

And then, out in the wastelands of Afghanistan to show off Stark Industries' latest bit of killing technology, the military convoy he's riding in gets ambushed; just before it explodes, he sees on an incoming missile his own company's logo. Next thing he knows, he's in the camp of a local warlord whose arsenal is stacked with Stark hardware, and who greets him as "the most famous mass murderer in the history of America" – a verdict that gets anecdotal backing from Yinsen, the grave, friendly surgeon who has saved Stark's life. All of a sudden, we're not in Kansas any more.

Watch the trailer for Iron Man

The ironies keep coming: asked by the warlord to build him missiles, Stark refuses, and is immediately subjected to a near-drowning – isn't that the kind of thing it's OK for Americans to do to suspected terrorists? Stark responds by pretending to build a missile – in fact, with Yinsen's help he's building an armoured exo-skeleton, complete with superstrength, flame throwers and jet boots. When the time comes for escape, Yinsen sacrifices himself so that Stark can get the armour booted up, dying with a touching speech about looking forward to seeing his dead family again – almost certainly the first time Hollywood has shown a Muslim embracing the afterlife in a heroic light.

It's a shame that, as the narrative develops, the permissible ethical implications shrink. Stark realises that the arms industry is a bad thing, and builds himself a sleek new suit of armour to start fighting evil. But his moral awakening is strictly limited: he now sees the peril of letting weapons get into the wrong hands; the thought that there may not be right hands doesn't seem to occur.

All the representatives of the US government in this film seem to be decent, straight-arrow types, from the grunts killed defending Stark in Afghanistan, through his air-force chum "Rhodey" (Terrence Howard), to the mysterious agents who keep popping up trying to make appointments with Stark: this last lot come from a secret government agency, with the cumbersome title of the Strategic Homeland Intervention, Enforcement and Logistics Department – an in-joke there for Marvel Comics fans. Pleasant change though it is to come across a film in which government isn't represented as a hive of murderous conspiracy and corruption, the characterisation implies an insouciance about government power that's at odds with an angry speech Downey gets to make about being part of a system of zero accountability.

While it fails to follow through on its own political questions, though, the film does offer a more plausible personal account of superheroism. Like Tobey Maguire's Peter Parker in Spider-Man – the only other really satisfying superhero film – Downey allows you to see that the attraction of putting on the costume has less to do with a crusade than with having a terrific new game to play: with great power comes great irresponsibility.

Most of the time, the film's shortcomings as dialectic are camouflaged by the acting. As well as Downey, you get Jeff Bridges as Stark's corporate fixer, Obadiah Stane – fun to watch, even if you don't sense a burning commitment to the character. You also get Gwyneth Paltrow as his factotum, Pepper Potts, excellent at exchanging neatly timed sarcasm with Stark, a shade less convincing at suggesting buried yearning towards her boss. Towards the end, though, the leisurely character development, is junked in favour of biff-pow action. That's obligatory, I guess, and Jon Favreau's choreography is competent: I particularly liked the contrast between Stark's Mark 2 armour, dainty in red and gold, and his super-enemy's clunking grey Mighty Joe Kong outfit.

But the ending leaves the story feeling oddly hollow and unnecessary – an opener for the franchise, rather than an event in itself. Still, Iron Man manages to be both a lot of fun, and quite possibly the most effective commentary on the war on terror that Hollywood has produced so far – not the best argued or the most committed, but the one that most people will see, and think about. You may go in for the Iron, but you'll stay for the irony.

Anthony Quinn is away