Watch an interview with Iron Man star Robert Downey Jr

Iron Man is the first blockbuster movie of the summer, and, despite the topical Taleban atrocities, it’s a roaring fairground ride. The director, Jon Favreau, has transformed Stan Lee’s 1960s comic strip into a creamy, live-action thriller. The story of a gifted geek who conquers his demons to save the world is a regulation Marvel Inc. fantasy. But the opening scene, showing American soldiers in a battle with Afghan insurgents, is a sour and shocking surprise.

These grim and bloody moments make the film feel older than its 12A years. But the stunts and special effects are a serious joy. The casting of Robert Downey Jr as the playboy hero and inventor of Iron Man is a sublime piece of mischief. Tony Stark is a Molotov cocktail of glamour and scandal, and Downey is all too convincing as the billionaire bachelor. The celebrity arms dealer is as frivolous and mad as Howard Hughes. His ingenious state-of-the-art weapons are the deadly tools that supposedly keep America safe, but he is far more interested in pinching a shapely pair of buttocks.

“Are you Leonardo da Vinci, or the Angel of Death?” asks an angry young blonde from Vanity Fair. Poor old Gwyneth Paltrow has to sweep these impressionable young journalists out of Tony’s water bed the following morning. She is Miss Moneypenny in Tony Stark’s empire, and her crush on the hunky charmer has got her nowhere. But despite his flash cars and the pole-dancing stewardesses on his private jet, she knows he has a golden heart.

The film hinges on the fact that Tony is blasted to bits after a weapons demonstration in Afghanistan. He is captured by the Taleban, locked in a cave, and kept alive by an electromagnet (run on a car battery) plugged into his chest that keeps the metal shrapnel from piercing his heart. In his cave he assembles an armoured suit out of old bomb cases. The film’s terrific effects kick in when Tony blasts his way to freedom in his bombproof shell suit. He has rockets in his boots, and flame-throwers in his metal wrists. The magical science is the stuff of gadget wonderland. The saving of Tony Stark’s soul comes a distant second.

This is where Jeff Bridges’s bald and brilliant creep, Obadiah Stane, comes into his own. Stane is Stark’s whispering mentor and business partner, who has made a pile out of secondhand neutron bombs. His poisonous and beefy influence is a gripping chill. I enjoyed this film far more than I really meant to. Favreau has done a magnificent job to keep his characters at a cartoon distance, while persuading the audience to believe in them.

12A, 126mins

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010