How was this going to work?

All those Marvel superheroes, many of them with their own action franchises, packed into one epic, save-humanity adventure.

How will the retro patriotism of Captain America mesh with the flippant cynicism of Iron Man? Could the brooding Hulk bond with the regal brawn of Thor?

How could anybody balance the interconnection of back stories, the clash of personalities, the need for shared screen time, the utter necessity of building up a villain capable of putting fear in this fearsome foursome and then some?

But it works, because Joss Whedon (“Buffy the Vampire Slayer”) brought his A-game to “The Avengers.” It works because he never loses sight of the fragile humanity of the characters, even in their special effects brawls. It works because somebody finally got The Hulk’s blend of rage, guilt and bull-in-a-chandelier-shop fun just right.

Nick Fury (Samuel L. Jackson) has created S.H.I.E.L.D., his super-secret superhero agency, mainly on paper. But when his minions recover the magical cube, the Tesseract, from where Captain America buried it last summer, Loki (Tom Hiddleston) and The Other (Alexis Denisof) plot Loki’s vengeful conquest of the Earth. Fury has to get the band together, get them to work as a team.

“We have our orders,” Captain America (Chris Evans) intones. “We should follow them.”

“Following’s not really my style,” Tony “Iron Man” Stark (Robert Downey Jr.) quips.

“You’re all about style, aren’t you?” the red-white-and-blue goody-two-shoes Captain fires back.

In an ensemble piece, Downey’s brilliant touch with the throwaway putdown is showcased to its best effect. He calls Thor “Point Break” (a surfer-Patrick Swayze hair joke) and “Shakespeare in the Park,” and asks “Doth your mother know you weareth her drapes?”

The earnest Evans gives just enough gravitas to the Captain, who understands how their special gifts are “a terrible privilege.”

Loki turns a couple of S.H.I.E.L.D. agents — the bow-and-arrow-wielding Hawkeye (Jeremy Renner) and Professor Selvig (Stellan Skarsgard) — into his flunkies, and sets about creating a means for an army of aliens to show up and enslave humanity.

Hiddleston grows into the part that seemed like a weak link in “Thor,” and makes the most of this guy’s megalomania and bad-guy bravado. “You are MADE to be ruled. Kneel before me,” he orders one and all. “It is your natural state.”

The real fun here is in the fractious nature of the superhero team — Iron Man sniping at and brawling with Thor, Iron Man’s quarrels with Captain America, the “issues” between the assassins Black Widow (Scarlett Johansson) and Hawkeye, and the “Serenity Now” ethos that Bruce Banner embraces lest “The Other Guy” (The Hulk) break out and make a mess of things.

Mark Ruffalo gives Banner/ Hulk a wonderful, almost passive “Nobody really should mess with me” pose, and he can trade wisecracks with the best of them. “That guy’s brain’s a bag full’a cats,” he says of Loki. “You can smell crazy on him.”

Whedon manages to give a staggering number of characters their “moments,” from Clark Gregg, the long-suffering agent whose thankless job it is to ride herd on the superheroes, to Gwyneth Paltrow’s sexy paramour/ assistant to Tony Stark, Pepper Potts. She’s all cut-off jeans and come-hither come-ons in their scenes together.

As you might expect from a movie with this many characters and that many zingers, “Avengers” is entirely too long and entirely too chatty. The 3-D adds nothing to it, and we lose the urgency every time we lose track of the menace and the villain.

But Whedon has managed a feat akin to last summer’s “Thor,” finding the fun in what should be, by any rights, an exhausted genre. “Avengers” isn’t deep (yes, we really should all work together) and it doesn’t reinvent the comic-book movie. But it is fun, and if it’s an indicator of the season of cinema to follow, this summer is going to be epic.