By JAMES DAWSON

Front Row Features Film Critic

Like Tony Stark’s Malibu mansion, the Iron Man movie franchise goes over a cliff with this disappointing third outing. The first “Iron Man” wasn’t perfect, and “Iron Man 2” had even bigger problems. But even though “Iron Man 3” is likely to find box-office gold thanks to the public’s affection for the Marvel Comics character and the star who plays him, this latest installment is a lead-balloon clunker.

That’s despite the fact that charismatic Robert Downey Jr. still seems perfectly cast as billionaire inventor Stark, the wisecracking full-of-himself smartass who is Iron Man’s alter ego. The problem is that the screenplay in which Downey is trapped, co-written by director Shane Black and Drew Pearce, is an ungainly contraption that is anything but a well-oiled machine.

There’s something here to displease everyone from hardcore Marvelites (who should be outraged by the way the movie utterly ruins the Iron Man comic-book’s signature villain) to casual superhero fans (who will be irritated by how little time Downey spends in his armor) to little kids (who may be traumatized by incidents of mass murder, torture and general sadism, when they’re not being bored).

Sir Ben Kingsley appears as the Osama bin Laden-like baddie known as the Mandarin, who commandeers the public airwaves to make menacing terrorist threats. But in a bizarrely wrongheaded change that completely subverts the character and sabotages the movie, the Mandarin later is reduced to neutered comic-relief status.

Considering that the comic-book version of the Mandarin has been around since the Iron Man comic debuted in the 1960s, it’s as if the makers of “The Dark Knight” had decided it would be a nifty idea to portray the Joker as nothing more than a toothless stooge. What’s most unfortunate about this Mandarin is not that his creaky seen-it-before particulars date back at least as far as “The Wizard of Oz.” What’s worse is that the movie trashes the Mandarin name, throwing away half a century of comic-book heritage for the sake of a dumb gag.

The change obviously was made in the name of political correctness, considering that the comic-book Mandarin could be regarded as Fu Manchu-level offensive to Asians. There’s also the fact that China has become such a big international box-office market that a different cut of “Iron Man 3,” featuring a Chinese actress who does not even appear in the US version, will be released in that country. Still, it’s too bad the producers didn’t rise to the challenge of making the troublesome stereotype shocking but somehow credible in a present-day context.

Gwyneth Paltrow returns as Stark’s brainy blond girlfriend and the head of his high-tech company. She gets to be both damsel in distress and an action figure in her own right this time around. Don Cheadle is back as Col. James Rhodes, aka the military’s red-white-and-blue version of Iron Man, whose name has changed from War Machine to Iron Patriot. Jon Favreau (who directed the first two “Iron Man” movies) returns for some annoyingly flat funny business as Stark Enterprises head of security Happy Hogan.

Newcomers include Rebecca Hall as a scientist whose 1999 one-night stand with Stark has nasty present-day repercussions (although thankfully not of the “Tony Jr.” variety). Guy Pearce is a vindictive scientist who is up to no good in a big way. Ty Simpkins is an annoyingly precious kid Stark meets in a Tennessee small town, because the producers apparently thought what audiences really want to see are scenes featuring an out-of-costume middle-aged man hanging out with a boy in a barn.

While footage featuring Stark without his armor and helmet gives superstar Downey what is literally more “face time,” it’s frustrating to watch him spend so much of the movie out of costume. Logic gaps also abound. The main one involves Stark wasting so much time improvising MacGyver-like hardware-store inventions instead of simply accessing his Iron Man equipment. A segment in which street-clothes-wearing Stark and Rhodes sneak into a henchmen-guarded Miami mansion plays like something out of a cheesy buddy-cop TV show.

“Iron Man 3” acknowledges events from last year’s excellent “The Avengers,” a movie that may have set the bar impossibly high for all other superhero flicks. Stark now experiences uncharacteristic and unconvincing anxiety attacks whenever he recalls his near-death experience in that adventure.

“Nothing’s been the same since New York,” he laments, noting that next to gods and aliens he is “just a man in a can.” Yet he bafflingly never tries tapping either his fellow superheroes or the resources of the global crime-fighting organization S.H.I.E.L.D. to combat the Mandarin and his monstrous associates, even after Stark’s home is destroyed, his friend is rendered comatose, the president is threatened with assassination and the public body count keeps rising.

Director/co-writer Black can’t forge what are supposed to be grimly dark elements (including mass-destruction explosions that reduce victims to Hiroshima-style wall shadows), sitcom-bland man-boy moments (potato gun, anyone?) and campy farce (the movie’s misbegotten Mandarin) into an alloy that has any structural integrity. A fireworks-like finale, in which Stark basically leaves himself utterly defenseless for no conceivable reason, makes no sense whatsoever.

The movie does include some impressive action scenes. Stark’s magnificent mansion comes under a jaw-droppingly destructive missile and machine-gun attack, and it’s a kick to see a helicopter taken out by a grand piano. Later, Iron Man comes up with an ingenious if unlikely way to save a ridiculous number of Air Force One passengers who have de-planed in mid-air without parachutes.

The only other silver lining in this rustbucket is that its poor quality may make Downey want to suit up at least one more time, in order to exit the franchise on a high note. It would be a shame if this cobbled-together dud marked his last solo appearance as the comic-book character he has come to define.