For those only now becoming acquainted with Mr. Whedon, he is the pop-nerd god responsible for the TV shows Buffy the Vampire Slayer, Angel, Firefly, and Dollhouse; the feature film Serenity (a Firefly spinoff that is among the most criminally neglected movies of the past decade); and the wondrous web-short Dr. Horrible's Sing-Along Blog. Back in the day, he co-wrote the original Toy Story, and more recently he co-wrote and produced the deliriously inventive The Cabin in the Woods. Perhaps more to the point, he was the author of a by-all-accounts exceptional stretch of the comic The Astonishing X-Men.
Yet despite this exhausting C.V., The Avengers is Whedon's first true bite at the apple of mass appeal. It is my humble prediction that the masses are going to stay bitten.
Now it is true that if you don't like superhero movies, you probably will not like The Avengers, which features all the tropes that inevitably accrue to the genre: the flying and punching and force-beams and silly costumes. But if you are even modestly open to persuasion, Whedon's effort is right up at the top of the Marvel heap, with the first Spider- and Iron Man and the first two X-Men. Given the degree of difficulty inherent in the undertaking, it's an accomplishment only modestly short of a miracle.
The Avengers were first assembled by Marvel Comics in Avengers #1, back in September 1963, with the gang deciding to unite following some spirited scrapping between Iron Man and the Hulk. In Whedon's re-telling, the geometry of discord is considerably more complex: Captain America bickers with Iron Man, who bickers with Thor, who bickers with the Hulk, who bickers with Black Widow. It's like an episode of Desperate Housewives with repulsor rays. The only one not to join in the squabbling is Hawkeye (who goes by his street name of Clint Barton), and that's because he's genuinely trying to kill them all, having been psychically enthralled by the villainous Loki.
Loki, as you may recall from the movie Thor, is the scheming adoptive brother of that hero and, like him, an extraterrestrial who inspired Norse mythology and retains a decidedly retro—I'm talking helmet-with-curved-horns retro—sense of fashion. As the movie begins, Loki is stealing the Tesseract (a cube of infinite power that you may recall from Captain America: The First Avenger) from S.H.I.E.L.D. agent Nick Fury (whom you may recall from the aforementioned movies as well as two Iron Mans and a The Incredible Hulk). Loki's plan is essentially to go all Grand Inquisitor on the human race, freeing them of the burden of freedom and offering his own rule in its place.
It is to Whedon's great credit that he manages to corral this herd of competing plotlines into something resembling coherence. The movies leading up to the Avengers were widely divergent in tone and even genre, in particular the intergalactic antics of Thor and the pulpy, throwback heroics of Captain America. But Whedon turns these inherent tensions to his advantage, making a film that itself spans genres: a superhero flick, yes, but one that also dabbles in alien invasion and Mission Impossible-style superspydom.