Something amazing happened to me toward the end of “G.I. Joe: Retaliation,” opening today. This is about as far from an amazing movie as you’ll find these days. Think of it as belonging to a new category of Hollywood film in the world, the Throwaway Blockbuster.

The Throwaway Blockbuster should be defined thusly: the budget is huge ($185 million, they say, for this one), the special effects so elaborate and clangorous and the action pace so relentless that no matter what you think of it, you have to consider it a “blockbuster,” i.e. a film made for the sole purpose of lining people up around the (imaginary) block.

But it’s otherwise a throwaway. There are good things in it. Certainly there are good people in this one – Bruce Willis, Channing Tatum, Jonathan Pryce in a showoff doppelganger part allowing him to be evil and oily one minute and weak and abused in the exact same scene. Most of all, there is Dwayne Johnson – also known as the Rock – who has clearly acquired a reputation as Movie Franchise Helper. Just add the Rock to your tired old recipe and the audience will smell something cooking that whets its appetite.

We’re making our way through this spring’s Dwayne Johnson festival, with one surprisingly decent action number (“Snitch”) and the most tantalizing of all still to come, “Pain and Gain” in which he and Mark Wahlberg work for Michael Bay (yes, Michael Bay, stretching out) in a very quirky comedy co-written by Buffalo native Christopher Markus.

But only the precious few “G.I. Joe” fanatics will find anything to talk about hours later, much less days or even weeks.

The moment that truly amazed me – and is worth talking about or at least thinking about – happens toward the end: the G.I. Joes, after losing one of their own, are converging for a big push against their archenemy COBRA, whose quest for world domination has caused them to invent a new space satellite weapons system.

As I watched this happen, I suddenly leaned forward in my seat. There is a scene where nuclear apocalypse is used as an extortion device by COBRA to get the world’s nations to disarm completely, leaving COBRA’s new satellite weapons the only apocalyptic force out there. “This is really good,” I said to no one special. What writers Rhett Reese and Paul Wernick devised for this toss-off comic book sequel is an extraordinarily ingenious bit of world-bashing futuristic invention. It’s a clever and even suspenseful bit of plot thrown into a movie which is otherwise very noisily and briskly ho-hum.

But so bent is director Jon M. Chu on fulfilling expectations for nonstop action that it’s frenetically cross-cut with a G.I. Joe action scene. That’s the franchise after all.

Lovely. But if the director had resisted about three quarters of those cross-cuts, slowed things down a little and let that nuclear Armageddon scene play out with suspense intact and real pizzazz from the actors, he’d have had something which people might still be talking about next week, or even next month.

But no. As a consequence, the very real narrative ingenuity of writers Reese and Wernick barely registers because it whirls by too fast and furious to make an impression. And too, by then, the movie has established itself as megaplex filler for a holiday weekend – a surefire audience magnet, but one whose international take will obviate the need for American box office “legs.”

Johnson comes into this movie as the new G.I. Joe, an ambulatory man-mountain called Roadblock who’s the best buddy of Duke (Tatum). They play video games together when not fighting COBRA and deflect the adorable pile-on tactics of Roadblock’s two preteen daughters. But then duty calls. Pakistan has become a riot with a ZIP code. The cast has to muster up its weapons and catchphrases and rescue some hostages.

They’ve got “a lot to do on Mount Olympus,” as they put it.

So Dwayne the Rock takes over, enlists the help of Gen. Joe Colton – Bruce Willis – whose first name gave the “Joes” their name. They all fly to Pakistan to release the hostages, where there’s a deadly air strike that indicates something is really, really wrong.

“There’s only one man who could authorize a strike like that,” says Roadblock, “and I voted for him.” The Prez has some splainin’ to do. Which is not going to happen because the real prez is locked in a basement while his evil double has taken over. (Hey, any movie that gives Pryce a little showoff time is OK with me.)

All of which is played out with the Joes getting help from COBRA folk to prevent COBRA’s new weapons system Zeus from bringing the world to its creaking knees. Never mind why comic book movies still make world domination such a common ambition for movie villains in an era when governments have all they can handle keeping their treasuries solvent and their neighbors peaceful. It seems to me running such an omni-stress world would be an assault on one’s health requiring a full-time cardiologist, shrink, gastroenterologist and chiropractor for everyone involved.

The writers and actors all showed up to do their jobs in this movie. The director? That seems to me another story altogether.

G.I. Joe: Retaliation

Two and a half stars (out of four)

Starring: Channing Tatum, Dwayne Johnson, Bruce Willis, Adriannne Palicki, Ray Park.

Director: Jon M. Chu

Running time: 89 minutes

Rating: PG-13 for intense sequences of combat violence, brief sensuality, language and martial arts action.

The Lowdown: The G. I. Joe team loses one of their own but saves the world from the evil domination of COBRA.