There could have scarcely been a better person for the job of writer-director of the long-awaited superhero mash-up "Marvel's The Avengers" than Joss Whedon, he of former "Buffy the Vampire Slayer" fame and co-creator of the recent genre-busting groundbreaker "The Cabin in the Woods." Too many big-budget studio tentpoles hire three groups of dispassionate committee scribes to work on the screenplay, only for the finished product to resemble, in development, complexity and thematic richness, a five-year-old's stick-figure drawing. What's the point? It is a credit to Marvel Studios and Paramount Pictures, then, that they realized a strong, passionate, talented singular vision was what was needed to pull off something with the ambition and scope of "The Avengers." And so it goes that the title characters (and several peripheral ones) from 2008's "Iron Man" and 2010's "Iron Man 2," 2008's "The Incredible Hulk," 2011's "Thor," and 2011's "Captain America: The First Avenger" have finally joined forces. By themselves, the quality of their films has ranged from solidly proficient to dud-worthy, none coming close to the upper echelon of the genre reserved by 2002's "Spider-Man," 2003's "Hulk," 2006's "Superman Returns," and 2008's "The Dark Knight." Together, under a fresh new eye, they are at once their same old selves and suggestively on the verge of being revitalized beyond simply "good enough." "The Avengers" may be slightly overstuffed, and it may not be the game-changer of Whedon's best work, but it's also far from the underdeveloped, soulless hodgepodge one might have feared. When it takes off, the results are pretty awesome.

Deep in the laboratories of the S.H.I.E.L.D. organization, valiant studies being done on the Tesseract, a powerful, potentially globally destructive energy source and portal, are cut short when disgraced Asgardian Loki (Tom Hiddleston)—wayward brother of warrior Thor (Chris Hemsworth)—breaks through. Equipped with mind-controlling abilities that promptly brainwash expert archer Hawkeye (Jeremy Renner) and scientist Dr. Selvig (Stellan Skarsgard), Loki steals the Tesseract and flees, hellbent on domination. With nothing less than the entire planet at stake, S.H.I.E.L.D. director Nick Fury (Samuel L. Jackson) decides it's time to gather together an army of superheroes who might be able to defeat what they wouldn't be able to by themselves. Cue the gathering-together of charmingly pompous Tony Stark/Iron Man (Robert Downey Jr.); former WWII soldier Steve Rogers/Captain America (Chris Evans); the in-hiding Bruce Banner/Incredible Hulk (Mark Ruffalo); butt-kicking Russian spy and field agent Natasha Romanoff/Black Widow (Scarlett Johansson), and, finally, Thor. Floating high above the clouds on a flying aircraft carrier, the disparate superheroes bond, clash, playfully rib, and ultimately assemble as they prepare for the battle of their lives.

Even with so many characters to contend with, "Marvel's The Avengers" feels like a complete motion picture rather than a greatest-hits montage, and that may be its biggest achievement. Writer-director Joss Whedon displays an understanding and affinity for his rag-tag good guys, even if this particular story shortchanges some of their personal conflicts and mostly uses them as brawn over personality (Steve Rogers, who is still dealing with waking up from a frozen slumber seventy years in the future, comes instantly to mind). Nagging issues pop up here and there—most significantly, the second act, filled with a lot of waiting around, could have either used more substance or a judicious editor—but character interactions are peppy and in good humor and the visuals are nothing if not impressive (the majestic aforementioned aircraft carrier in the sky isn't something a person sees every day).

Attention-grabbing from the get-go before a temporary bout of meandering takes over, the film eventually kicks into gear with a rousing, stomach-dropping aerial set-piece that literally wows. From there, it's off to New York City for the final showdown as a full-on alien invasion escapes from the Tesseract's open gateway. Fans waiting for the requisite fireworks get them here tenfold, the simultaneous banning-together of Iron Man, Thor, Captain America, Incredible Hulk, and Black Widow an unforgettable sight to see. Whedon, cinematographer Seamus McGarvey (2011's "We Need to Talk About Kevin"), and editors Jeffrey Ford (2011's "Monte Carlo") and Lisa Lassek mount this complex sequence with far more coherence than Michael Bay ever could, favoring rhythm and suspense and payoffs over empty, clanky bombast. Several individual shots are especially audacious, one that zooms around to pick up the actions of each character at the same time beyond impressive. In addition, at least two moments with the out-of-control Hulk should have audiences spontaneously and uncontrollably cheering.

The cast finds all the heavy hitters returning, save for the allegedly difficult, power-hungry Edward Norton (Mark Ruffalo takes over the part of Bruce Banner/The Incredible Hulk). Robert Downey Jr. (2011's "Sherlock Holmes: A Game of Shadows") is as smarmy and somehow likable as ever, his early scene with Pepper Potts (Gwyneth Paltrow) reclaiming all of the easy chemistry they shared in the first "Iron Man." Paltrow's screen time lasts for two scenes and maybe five total minutes, and yet she makes a far better and lasting impression than she did in the woeful "Iron Man 2." As Steve Rogers/Captain America, Chris Evans (2011's "What's Your Number?") isn't given nearly enough to do and almost no facets of his character to explore, but he certainly fills out a tight white tee with the best of them. Chris Hemsworth (2009's "Star Trek") somehow looks even more faithful to his character than he did in "Thor," a hint of ferocity and machismo that wasn't quite at the same level in the earlier film. After being introduced and then summarily wasted in "Iron Man 2," Scarlett Johansson (2011's "We Bought a Zoo") actually does see an uptick in development for Natasha Romanoff/Black Widow, and with every punch and drop-kick she earns her place among the boys. Jeremy Renner (2011's "Mission: Impossible - Ghost Protocol"), who made a cameo in "Thor," also gets a substantial increase in material as Hawkeye; he's such a force in front of the camera that it doesn't even matter that he's playing the protagonist with the least amount of fanfare.

On the other hand, Mark Ruffalo (2010's "The Kids Are All Right") is disappointing as Bruce Banner; when green and huge and CGI'ed, he's the movie's rock star, but the usually reliable actor underplays the non-transformation scenes with a low-key, laid-back tone that leaves him an afterthought. As sniveling villain Loki, Tom Hiddleston (2011's "Midnight in Paris") makes up for a comparitively undaunting physical appearance by being downright hateful. One cannot count the seconds fast enough until he receives his comeuppance. After appearing in most of these Marvel movies without ever getting a chance to do much of anything, Clark Gregg (2011's "Mr. Popper's Penguins"), as steadfast S.H.I.E.L.D. agent Coulson, finally comes into his own, garnering a first name (Phil), some welcome nuances, and a couple great little moments in the spotlight. It stands out because it's so happily unexpected, a surefire sign that this project was no cash grab for Joss Whedon. Finally, in a rather needless addition to the ensemble, Cobie Smulders (TV''s "How I Met Your Mother") is Agent Maria Hill, sashaying around in form-fitting pants and stiffly delivering no-nonsense dialogue.

As the first of 2012's summer blockbuster hopefuls, "Marvel's The Avengers" is a crowd-pleaser through and through. It's thrilling when it wants to be, it's got star power to spare, and the action and effects are top-notch. Is it a new comic book adaptation classic, though? No. The plot is pedestrian as far as these things go, and it's a bit too unwieldy for its own good. If the Marvel films that this one derives from have been more technical exercise than lingering emotional experience, maybe it has to do with their overall safeness and devotion to convention. As Manhattan gets destroyed during the climax, there are various shots of people running away from fireballs and falling debris. There is no real weight or gravity to this impending danger, though, save for in two brief shots, one of a frightened Pepper and the other of a helpless Maria solemnly watching the destruction on television. It's a pretty obvious callback to 9/11, but it works because of its underlying connection to reality. Going forward with all of these respective franchises, there should be a deeper threat to the Marvel-verse that sets them apart from the pack. Room for improvement is still immense, but "Marvel's The Avengers" is a baby step in the right direction by a guy who knew what kind of film he wanted to make, and made it. If the post-credits coda is any indication (and you know that it is), a sequel—and another chance for greatness—can't be far behind.