Robert Downey Jr. tests out his armor in the superhero adventure Iron

These comic-book movies, they all start the same, with that montage of Marvel animated heroes. They all end the same. You know what I’m talking about.

But darned if “Iron Man” isn’t everything a summer movie should be, and more. The first big popcorn movie of the season is also the best Marvel movie since “Spider-Man,” a silly-serious pedal-to-the-metal (ahem) E-ticket ride with, now get this, a message.

“Spider-Man” said a little about the morality of violence, the heady egoism of fame and the consequences of doing nothing when danger faces others. Iron Man is about war and the “zero accountability” crowd that profits from it.

This serious subtext leaps out of the very first moments of the film. The swinging, hard-drinking, fast-talking arms merchant Tony Stark (Robert Downey Jr.) does a ride-along, in Afghanistan, to show the military Stark Industries’ newest toy, the Jericho missile, a weapon that makes walls, and mountains, come tumbling down.

“They say the best weapon is one you never have to fire,” Stark riffs. “I prefer the weapon you only need to fire once.”

But that big-boom test is followed by an ambush, and Tony Stark, “merchant of death,” is taken prisoner. He sees, first hand, what his ordnance does to the world and the people in it.

“Those are my guns,” he gripes to the Taliban-ish guerrillas. “Where’d they get my guns?”

Stark, a tech whiz, eventually engineers his escape from this Afghan cave of certain death, but not without damage. He’s got to have this glowing “arc reactor” in his chest to keep shrapnel fragments from migrating into his heart. He’s lost his appetite for weapons of mass destruction. And he has this neato idea for a suit of armor that will set things to right.

The first place “Iron Man” goes right is in the casting. Downey brings not only his hard-partying baggage and sense of play to Stark, he finds his pathos, too. They cast Jeff Bridges, who shaved his head to play Stark’s No. 2 man at Stark Industries, to play a character with shades of gray in his movie aura. Terrence Howard is the Air Force colonel who was Stark’s college pal, and Oscar winner Gwyneth Paltrow further classes up the joint as the sexy assistant, Pepper Potts, whose brains make her too smart to fall for her womanizing boss’s come-ons. For now.

Superhero comic-book movies all share a gravitas problem, one most directors cope with by emphasizing the darkness – shadows, Gothic production design, haunted characters. “Iron Man” director Jon Favreau’s treatment (four writers were credited) leans the other way. He is so in sync with Downey’s playful, eccentric take on his line readings and earnest but jokey performance that he lets Downey throw away more clever banter than most comic-book movies can manage to keep. That makes Stark’s battlefield conversion, his moments of uncertainty and pain, stand out.

Downey’s Stark is glib and abrasive, and he’s ready with a quip when somebody insults him back.

“Deflect it, absorb it, but don’t send it back to me!”

If you don’t want to party, don’t bother climbing into his Humvee.

“I’m sorry, this is the Fun-vee. The Hum-drum vees are back there.”

But every death carries emotional weight, every semi-serious flirtation between Stark and Potts has pangs of lonely romantic longing. This is what you get when you throw great talent at decent material. They make it sing.

At some point, every “Hulk”/”Spider-Man”/”Fantastic Four” and “Iron Man” devolves into “Robocop,” that big finish fist-fight between superhero and supervillain. But everything up until then, from the funniest Stan Lee cameo ever to the inevitable suggestion that there will be a sequel – “Next time” – is a pitch perfect whoop. Christian Bale may have made superhero movies safe for serious actors. Downey makes them fun.