Iron Man 2 (12A)

This didn't take long to rust. The gleam on the first Iron Man movie two years ago was less to do with the clanking hardware than its steely refusal to play the usual superhero game.

It posited the outlandish idea of an American weapons entrepreneur and playboy billionaire who directs his genius away from war towards philanthropy, incarnated in his armour-plated alter ego Iron Man. The look, part-RoboCop, part-Darth Vader, wasn't especially original, but the casting was. Robert Downey Jr, mercurial and mischievous as Tony Stark, set the whole tone of the film and restored something we hardly saw in action blockbusters anymore: a sense of fun.

Well, you can say goodbye to that. Where the first film was droll and fleet-footed, the sequel is nervy and distracted, eager to replicate the original's success but clueless as to how to go about it. From the bluster of the opening set-piece you can feel the film-makers' strain: heavy rock, dancing girls, crowds going pointlessly wild. Tony Stark, playing up to his national-hero status, has become a showman, or should that be a show-off? "I'm not saying that the world is enjoying its longest period of uninterrupted peace because of me" – except that he is saying that, later boasting to a senate arms committee that he has successfully "privatised" world peace through his iron-clad policing.

Tony fights off the Pentagon brass, who want to appropriate his Iron Man technology in the interests of national security, but there are more problems on the horizon. First, a disgraced Russian physicist named Ivan Vanko is out for revenge, convinced that Stark Industries ripped off his father's Iron Man prototype. That he's played by Mickey Rourke with jagged gold teeth and spark-spitting whips that can cut a car in half should be scary, or funny, or funny-scary, but his menace is diluted by his smarmy sponsor Sam Rockwell, playing a rival entrepreneur. Second, Tony's blood toxicity levels are climbing dangerously – all that iron – and seem to induce behavioural swings that surpass even his legendary standards. Things get so out of hand at his birthday party that his pal Rhodey (Don Cheadle) is compelled to don an Iron Man suit and bring the celebrations to a shattering halt. Third, Tony has promoted his superefficient Girl Friday "Pepper" (Gwyneth Paltrow) to his company's CEO, thereby sublimating the romantic attraction that crackled between them in the first film.

Is that enough to be going on with? Wait, there's more. It seems that Tony also has family issues, specifically a father who – you'll never guess – didn't love him enough. (He's played in flashback by John Slattery, aka Roger from Mad Men). You get the feeling that the scriptwriter Justin Theroux might have an attention-deficit disorder, because he doesn't seem able to let 10 minutes pass without introducing a new angle, or a new character. For instance, Scarlett Johansson makes one of her sultry entrances as a personal assistant, and just as we're getting used to that she transforms herself into a high-kicking, ass-whupping martial-arts queen called Black Widow. As for Samuel L Jackson playing "Nick Fury", the leather-coated dude with an eye-patch, it's anyone's guess what function he's meant to be fulfilling. These two appear to have crashlanded from another movie altogether. Actually, that's precisely what they have done: both are Marvel Comics characters who've been parachuted in as teasers for the forthcoming Avengers.

Iron Man 2 could certainly use some clarity. Halfway in, the narrative is more crowded than rush-hour on the Northern Line. You notice, too, that as the big set-pieces gain in noise and scale they dwindle in enjoyment. The ding-dong between Stark and Vanko on the Grand Prix circuit at Monaco has a brutal sort of bewitchment, but the fights thereafter are just a lot of junkyard scraps; I was more than once reminded of Michael Bay's moronic orchestrations in Transformers. There will be viewers awed and thrilled by this mechanical mayhem, but I suspect that few of them will be above the age of 13.

The single point of interest is to see whether Downey Jr can rouse himself to carry the movie, as he did first time around. With his Van Dyck beard and just-toned-enough body he's looking good at the moment – hell, given his past record of addictions, drug busts and prison time, he's looking great. Maybe they should call him Irony Man. Sadly, even he looks a bit out of sorts here, gabbling through many of his speeches and looking slightly bewildered by what's happening around him. (Join the club). The will they/won't they? vibe between him and Gwyneth Paltrow is a fizzle. I laughed a couple of times at the start when Tony twits a disobliging senator, played by Garry Shandling, first by greeting him "Hello, dear", then cheekily offering himself as Secretary of Defence. But it's thin reward for nearly two hours. The movie sort of betrays the inventive whiz, too, because it's really not his ingenuity that's at stake anymore. The climactic fight comes down to a hardware contest, and Tony just happens to have better toys than the baddies.

‘Iron Man 2’ - What do you think of the long-awaited sequel? Email your reviews (40 words plus) to cultureclub@indepedent.co.uk or post them in the comments section below.