The summer movie season starts out with a bang—lots of bangs, actually—with genre-master Joss Whedon’s explosive, and often explosively funny, take on Marvel Comics’ flagship multiple super-hero title. “The Avengers,” which follows individual pictures for The Hulk, Captain America, Thor and Iron Man (two recent ones for the latter, in fact), and adds Nick Fury, Hawkeye and Black Widow for good measure, is the best big-budget hot-weather blockbuster to hit theatres since J.J. Abrams’ reboot of the then-moribund “Star Trek” series.

This is essentially an “origins” movie, which in the super-hero category can be deadly. But Whedon skirts the pitfalls by slyly setting off the characters’ disparate personalities, setting up rivalries and animosities that he then employs to amusing effect, while at the same time concocting a world-threatening menace they have to join forces to combat. The danger is posed by Thor’s ne’er-do-well brother (or adopted brother, as the Asgardian points out at one perfectly-chosen moment) Loki (Tom Hiddleston), who plans to launch an assault on the planet with an extraterrestrial army. To do that, however, he needs to gain control over the Tesseract, the energy source discovered in “Captain America” and now lodged in Fury’s SHIELD headquarters, where it’s protected by him (Samuel L. Jackson), Hawkeye (Jeremy Renner) and the Widow (Scarlett Johansson) while being examined by Professor Selvig (Stellan Skarsgard), Thor’s friend.

The theft, which also involves Loki’s turning Hawkeye and Selvig into mind-controlled minions, leads Fury to summon billionaire industrialist Tony Stark, aka Iron Man (Robert Downey, Jr.), super WW2 soldier Steve Rogers, aka Captain American (Chris Evans), hammer-wielding alien Thor (Chris Hemsworth) and scientist Bruce Banner, aka The Hulk (Mark Ruffalo) to his behemoth airship. There the first three—wisecracking Stark, ultra-earnest Rogers and bombastic Thor—bicker and jockey for position while Banner, who fears getting angry and having what he calls “the other guy” emerge, works to pinpoint Loki’s location. It’s not until Hawkeye attacks the ship with Loki’s allies that they all bond—though not entirely happily, especially since the death of a colleague adds a touch of communal regret—to meet the challenge as a unit.

Despite a bit too much exposition about the Tesseract, Whedon gets a lot of mileage out of this first half of the picture, with an uncanny knack for inserting a bit of funny business that stays on this side of spoofing at just the right moment (witness Thor’s “adopted” line). The preening Downey gets the lion’s share of laughs, of course, but Evans and Hemsworth expertly play straight men to him, while the others handle their assignments with skill, even if Jackson—as usual—has a tendency to bellow and Hiddleston’s penchant for camping it up can go to extremes. And though Johansson is somewhat underutilized, Clark Gregg gets to shine as Fury’s second-in-command, and Ruffalo proves a surprisingly apt choice to play the sad-faced Banner, giving the character a depth that neither Eric Bana nor Edward Norton (not to mention Bruce Bixby) managed in earlier incarnations. When The Hulk finally emerges, in a big tete-a-tete with Widow, it momentarily seems that (once again) the animated thing isn’t going to be a very good fit in the live-action material, but it turns out Big Green plays well with the other heroes, and that by appearing more sparingly than in solo stories he actually cuts a larger figure.

And though this initial segment of “The Avengers” concentrates on dialogue and exposition, Whedon never neglects to give us infusions of action, though some of it (like the first battle between Thor, Iron Man and Captain America over Loki) has lots of humor to it, as does Hawkeye’s attack on Fury’s airship—though in that case the balance is on the action side). The picture’s second half, in which Loki unleashes his assault on New York, the action definitely predominates, although chuckles are never entirely absent.

One could argue that this later section of the movie does go on and on, with a couple too many of those huge dragon-like monsters coming through the portal from the alternate universe and way too many sled-flying alien soldiers biting the dust. Admittedly when you have a whole troupe of super-heroes engaged, each of them has to be given adequate time to do his or her thing—and that means a certain degree of repetition and an inordinate number of triumphant climaxes. Still, though some of us could certainly have done without yet another of Stan Lee’s tiresome cameos, Whedon manages to pull it off better than one has any right to expect, providing not only a satisfying conclusion but a nifty postscript (as well as a hint about the next installment during the final credits that will undoubtedly make fanboys salivate).

It can now be taken for granted—after Marvel’s previous single-character hits—that “The Avengers” is handsomely mounted, with crisp cinematography by Sheamus McGarvey, classy if not ground-breaking effects from a bevy of companies (all overseen by Janek Sirra and Jeff White), and editing by Jeffrey Ford and Lisa Lassek that’s crisp enough to make even a 2½ hour running-time feel only slightly too long. The music by Alan Silvestri is disappointingly unmemorable, but the visuals and sharp writing make up for it. And the 3D format, though as usual it darkens the images, is less damaging here than it often is.

“The Avengers” represents a project that, quite frankly, courted disaster. That it’s come off so well is really a tribute to Whedon’s genuine affection for the source and his uncanny sense of how to meld these very different characters into a unit while maintaining their distinctive qualities, while balancing action and humor as well as exposition and effects. He’s a fan who’s channeled his enthusiasm, which could have gone awry, to positive ends to fashion a movie that can communicate the excitement a lover of the comic book will experience watching it even to those who have never read a single issue.