Marvel’s The Avengers; PG-13, 155 minutes; Regal Seminole Square 4

It seems like a fine idea to put Joss Whedon in charge of Marvel’s The Avengers. Given his knack for wisecracking-ensemble revitalizations of chancy entertainment properties (there was “Buffy the Vampire Slayer” and then there was Buffy the Vampire Slayer), Whedon’s superhero summit, adapted by him and Zak Penn from Stan Lee and Jack Kirby’s comics, might well be the ultimate Marvel.

Less so is it a marvel, ultimately. Culled from their respective blockbusters, clad in flashy costumes and CGI, Captain America, the Hulk, Iron Man, and Thor (respectively Chris Evans, Mark Ruffalo, Robert Downey Jr., and Chris Hemsworth) have come together at last. As established by covert military administrator Nick Fury (Samuel Jackson), their ranks also include the archer Hawkeye (Jeremy Renner) and the martial artist Black Widow (Scarlett Johansson), who haven’t yet had movies of their own and don’t seem to need them.

So this amounts to an enormous, expensive juggling act. Contractually obliged to proceed from one set-piece to the next, The Avengers gathers at least enough momentum to not seem as long as it is. But it works best in the downtime, when we just seem to be hanging out backstage with some sort of action-figure supergroup. It’s sweet to see these characters treated with teasing reverence, as if little individual rituals of gentle ridicule can redeem the sheer silliness of posing them together.

Obviously Whedon wanted our heroes’ essential infighting, be it verbal or forest-flatteningly physical, to seem more personal than a mere din of clanging metallic collisions. Accordingly the best internal-battle scene involves Ruffalo’s scientist wringing his hands over that innate Hulkdom, which he says once left him desperate enough to put a bullet in his mouth—but “the other guy spat it out.” Clever strategy there: Tell, don’t show. Other Whedonisms include redemptive self-sacrifice as grand thematic theory and regrettable supporting-player sacrifice as operative practice. But he does understand that at the core of superhero mythology is the possibility of transcendence, even if it’s just an aircraft carrier managing to become an aircraft.

For the humans, reconciliation requires an external enemy, and our villain this evening will be Thor’s brother Loki (Tom Hiddleston), an arrogant extraterrestrial Viking with one of those bullies-are-secretly-insecure personalities and the sort of fascist urge that really gets Captain America’s goat. When Loki summons a war-mongering horde through a hole in the sky, the Avengers get to work dispatching disposable baddies as if from some technically sophisticated yet narratively forsaken video game. These invaders make more of a mess than a threat, but at least we can tell what’s going on: the climax.

What’s most fun is Loki’s suggestion to a throng of kneeling civilians that they’d be happier in supplication anyway. Might that also be aimed at hardcore fans of movies made from comics? As the T-shirt says, “Joss Whedon Is My Master Now.”