rated PG-13

“Iron Man” rocks. Okay, with that out of the way, let’s get to it.

There’s no secret about the troubled paths Robert Downey Jr. has traveled. In the not too distant past, when not circling the revolving door at the rehab center, he could often be found reading scripts delivered to his prison cell. At 42 years old, however, he has conspicuously cleaned up his act and come to be well recognized as one of the finest actors of his generation. But it ain’t the years, it’s the mileage. The 1,000 miles of hard road is still visible in this guy’s eyes, and casting him as a multi-zillionaire establishmentarian genius whose arrogance is rivaled only by his appetites belies an admirable shorthand in casting.

The first shot of “Iron Man” is a close up of Downey’s hand, as Tony Stark, untouchable heir to his family’s multinational arms manufacturing company, leisurely caressing a clinking tumbler of scotch, and it’s made directly evident that this is a man with weaknesses. Chauffeured by a contingent of U.S. Army personnel to a sales pitch in Afghanistan for his latest invention—a projectile capable of leveling small mountain ranges—he asks the camouflaged assembly, “Is it better to be feared or respected? And I’d say, is it too much to ask for both?”

Glib though it be, the line actually holds a remarkably subtle key to why Stark works as a modern superhero. In point of fact, he is neither feared nor respected. Beneath his depthless funding and atomic charisma, he knows he’s regarded merely as a hard drinking, high rolling, silver spoon sucking daddy’s boy. His drive to excess has made him a walking punch line. Echoing his life’s work in arms manufacturing, he wears his wit, wealth and egotism as elaborate mechanisms of defense, and, after an unexpected (if inevitable) attack by Afghani guerillas in which his body is riddled with shrapnel from an explosive piece of his own company’s merchandise, he realizes for the first time what poor protection he has against the evils of the real world. Captured by enemy forces, dragged through the dirt and into the darkness of a cold rocky cave, and forced at gunpoint to devise a WMD out of the guerillas’ stockpile of munitions, he does what any insecure prick in denial might do: he builds a better suit of armor.

And what a suit it is. His initial attempt, a lumbering, hand-wrought metal shell with chemical throwers spewing flames from the sleeves is almost comic (no pun intended, really) to behold, but plenty badass enough to blast his way through a dozen bad guys to freedom.

Returning home to his high-tech bachelor pad, a certifiable fortress of solitude on a lofty Malibu peninsula, Stark retreats to his basement workshop a changed man. Rallied by his first ever experience with real consequence and driven to finally take control of the powers at his disposal, his single-minded mission to upgrade the suit as a force for good in the world is clearly a reinvention of his own damaged self.

But enough with the 12 steps. Flying far above all this armchair psychology is the fact that this flick is an rocket-fueled thrill ride. First of all, it’s often downright funny. Downey plays Stark like a wisecracking bastard child of Howard Hughes and Bill Murray raised by Wile E. Coyote. The construction and testing phase of the suit features a series of entirely startling Acme Factory moments, which pointedly remind that Downey got an Oscar nomination for his role as Charlie Chaplin.

With visual effects technology being what it is these days, it’s like crying wolf to even bother qualifying how seamless and groundbreaking the imagery is. But this one really is a tour de force, realized by an epic re-teaming of the computer wizards at Industrial Light and Magic with practical fabrication by Stan Winston Studios. These are the folks who respectively rendered all the effects for the “Pirates of the Caribbean” flicks and “Aliens” (Ripley’s loader now stands as the official great grandma of cinema’s mechanized suits). In 30 years, the talented artists of Marvel’s “Iron Man” comic books never managed to drive home so flawlessly that this man has forged himself into a living missile.

When the completed hot rod costume is finally installed, enclosing Stark in a whole new definition of “full metal jacket,” and Iron Man at long last fires up the repulsors and lifts off, it’s with a breathless rumbling power-gasm and real sense of danger. Rocketing back to Afghanistan to defend the rights of the defenseless, Stark’s aggressive, pitiless anger toward his foes is a perfect emotional match to his newfound invulnerability. It’s positively menacing and completely believable. Unlike so many superhero getups we’ve seen before, this one plays less as a mask than it does as an extension of the character, and even with the full face helmet closed, completely obscuring all physical features, one still gets a distinct sense of Downey’s Stark within.

After the deluge of over-effected extravaganzas that have come to define the blockbuster season, as well as the strident and possibly misplaced efforts of filmmakers to recompose comic themes as dark, sullen affairs in the hopes that they’d be taken seriously, salutes to director John Favreau, and Marvel Studios (“Iron Man” represents the first time they’ve ever adapted one of their own properties for the big screen) for finally achieving a fabulous and entertaining balance of pathos, pith and projectiles.