Joss Whedon's The Avengers — not to be confused with Jeremiah Chechik's film of the same name, where Ralph Fiennes wielded an umbrella and saved the world from evildoers in candy-coloured teddy bear suits — is a mix of everything: of superheroes, of action and emotion and comedy, of staging that careens between prestige theatre and vaudeville, and of acting styles that span the spectrum from silent cinema to the modern day.

To get an idea of the overall mood, you have to imagine something starring Buster Keaton, Spencer Tracy, Sylvester Stallone and Marlon Brando, and directed by Michael Bay and Sidney Lumet on a bank of giant green screens. That gleaming cube at the centre of the screen could well be the kitchen sink — though it's really the Tesseract, a fearsome energy source, which Loki (Tom Hiddleston) wastes no time stealing, after which he proclaims, “I am burdened with glorious purpose.” For an instant there, the film itself seems freighted with glorious purpose.

Is there a better conductor of electricity up the spine than plummy villainy played with a British accent? Hiddleston, last seen in War Horse vanishing into a puff of smoke, creates such a devilishly theatrical character that we wonder not, as we usually do in these movies, whether the superheroes will be called upon to engage with a worthwhile supervillain, but whether this supervillain will be dispatched by superheroes worthy of him.

And those heroes come in all shapes and sizes. There's Hawkeye (Jeremy Renner), the master archer, and Black Widow, whose prime power appears to be that she comes in the form of Scarlett Johansson. Hulk (Mark Ruffalo), who'd retreated to Kolkata to lead a stress-free existence (this is how we know we're in the comic-book universe), returns with greying hair and a rumpled suit. Thor (Chris Hemsworth) reappears with his hammer, and Captain America (Chris Evans) shows up with his shield and a demeanour that could only come from being raised on a diet of apple pie.

Then there's Iron Man (Robert Downey, Jr.), the magnetic core of the entire enterprise. Not since Harrison Ford slipped into Indiana Jones has an actor so memorably ingratiated himself with a playful part — he is introduced alongside Pepper Potts (Gwyneth Paltrow), and their banter has a screwball-comedy vibe that sets the tone for the rest of his scenes. Downey, Jr. reminds us that special effects mean nothing unless the character inside the suit is a character, a fully formed human entity distinguished not just by a formidable superpower but by, say, the Black Sabbath T-shirt on his person (and, of course, Black Sabbath recorded a song named Iron Man).

Downey, Jr.'s Iron Man has the distinct attitude that most other superheroes lack, and it's tempting to imagine a movie-long contest between him and Loki, the winner being the actor who scarfs down the most scenery. He even punctures the pompousness of other superheroes, dismissing, for instance, Thor's grandiloquence as “Shakespeare in the Park.” Even as he soars, Iron Man keeps The Avengers grounded.

Whedon takes a leaf from Iron Man's manual and infects his film with a sense of mischief. Where Eric Bana and Edward Norton played glumly into the bifurcated angst of Hulk, Ruffalo locates a vein of slapstick comedy. There may even be a splash of unintended humour in watching Cobie Smulders (from the sitcom How I Met Your Mother) as a secret agent on what looks like the deck of the Starship Enterprise. It's too drastic a change of image — we expect her to trip over Thor's cape and rush red-faced to Johansson's side to whine about the embarrassment over a glass of Canadian red.

But Nick Fury (Samuel L. Jackson), the director of S.H.I.E.L.D, is left with little to do. We're promised an inscrutable character (“even his secrets have secrets”), but he's content to blend into the wallpaper as the Avengers save the world from Loki's minions, who arrive from outer space on ships that snake through Manhattan's airspace like sluggish alligators after a noonday meal.

Captain American wonders, at one point, if his stars-and-stripes costume isn't old-fashioned. He's told that, sometimes, “People might just need a little old-fashioned.” That The Avengers certainly is, resisting the modern impulse to peel back tormented layers of superhero psyche. What you see is what you get.

The Avengers

Genre: Action/fantasy

Director: Joss Whedon

Cast: Robert Downey Jr., Chris Evans, Scarlett Johansson

Storyline: A host of superheroes unite to save the world

Bottomline: Fun while it lasts