Film of the week: Transformers: Dark of the moon

Even the tweenie boys whose pocket money this special-effects showcase aims to steal will probably forget why they wanted to watch it by the third hour of mayhem

• Optimus Prime strikes a pose in Transformers: Dark of the Moon.Picture: PA Photo/Dreamworks

Transformers: Dark of the moon (12A) **

Directed by: Michael Bay

Starring: Shia LaBeouf, Frances McDormand, John Turturro

The first Transformers movie was a bar-lowering piece of incomprehensible metal-mashing mayhem that scored big with audiences and certain critics easily pleased by the sight of giant robots with a penchant for toilet humour. Its crassly commercial and wilfully dumb 2009 sequel, on the other hand, was almost universally reviled and yet proved so astoundingly successful that at times it felt like a deliberately provocative piece of performance art with a massive budget, one designed to test a) just how many members of the public would pay good money to watch something so pathologically incoherent and b) how many critics would take the bait and transform themselves into gibbering bundles of inchoate rage.

It may have remained perversely admirable in this respect alone had its success not facilitated Transformers: Dark of the Moon. Loud, long and lecherous, Michael Bay's third stab at dispensing the equivalent of a small country's GDP in the service of keeping a bunch of ADHD-afflicted 12-year-olds stimulated for close to three hours feels very much like a rambling bad joke to which no one can remember the punchline.

Announcing itself in typically brazen fashion, the new film ditches much of the gibberish mythology that was used to glue the action set-pieces in the previous instalments together and instead makes a bizarrely po-faced attempt to create a story that weaves the titular toy line-inspired giant robots into the fabric of 20th-century history via the JFK-sanctioned space race. Neil Armstrong's "giant leap for mankind" thus becomes - I kid you not - a giant leap to retrieve alien intel from a crashed Autobot spacecraft and, in what might constitute one of the most cringeworthy cameos ever, the real Buzz Aldrin puts in an appearance later on to receive props from good-guy Transformer Optimus Prime.

It's all a bit X-Men: First Class, but not in a good way, as archival footage of JFK, Richard Nixon, Walter Cronkite and the Nasa bods at mission control is spliced into re-enactment scenes shot using mock-vintage film stock. Flash-cut to ribbons to hide how poorly matched the doubles are to the real historical figures they're supposedly playing, it's the sort of goofy idea that might have worked were Bay not labouring under the misapprehension that it gives the film the kind of serious historical sweep that can justify its heinously excessive 157-minute running time and its militaristic flag-waving ending.That it doesn't is immediately apparent the moment the film rejoins the present day and the life of its hero, Sam Witwicky (Shia LaBeouf). Having twice saved Earth from Decepticon destruction (scoring a medal from a digitally rendered President Obama in the process), Sam is having a tough time getting a job in the real world now that he's graduated college. As plot points go, it barely supplies more than a couple of minutes' worth of drama, but that doesn't unduly worry Bay, who devotes much of the first hour to catching up on Sam's life as he whines about not being looked after by the government whose very asses he help save, while mooching off his girlfriend whose ass he's worried is being coveted by her handsome new boss.

That his girlfriend is unfeasibly hot almost goes without saying, though this one - played by British lingerie model Rosie Huntington-Whiteley - is much more submissive and doting than the one played by Megan Fox in the first two films. Fox was fired for likening Bay's tyrannical on-set presence to Hitler, and the director makes a couple of jokes at her expense, which - when combined with the fact that he's replaced her with a model who not only keeps her pouting mouth mostly shut, but is one step away from being a Stepford-style automaton - seems a depressingly reactionary warning that Hollywood won't tolerate actresses with the temerity to speak their minds.

But nobody goes to a Transformers movie to examine its sexual politics, and nor do they go for the story (Decepticons hatch fiendish plan to transform Earth into their home planet). They go for the mayhem and, after 100 minutes of choppily edited exposition, dismal slapstick and inconsequential subplots (featuring talented actors like John Turturro, Frances McDormand and a weirdly orange John Malkovich), Bay finally lets rip with a tide of devastation that turns Chicago into a war zone.

Buildings are folded in on themselves. People are hurled through the air. Giant robots blow other giant robots up and, for a little while, it's all so audaciously staged that even the stereoscopic 3D can't detract from it. Trouble is, it just goes on and on, to the point where it becomes impossible to distinguish who or what anyone is, why it's happening and why we should even care about what the outcome. It's war porn for kids and after stimulating the senses it eventually just numbs them.