'Avengers: Age of Ultron' (PG-13)

Joss Whedon has announced he won’t be making any more Marvel Studios movies — the five years he spent writing and directing The Avengers and its sequel, Age of Ultron, wore him out — which is too bad, because he was starting to get really good at it. Where the first film often bore the whiff of laborious obligation, reintroducing characters we already knew from other movies and explaining how they wound up fighting on the same team, the new movie gets to the fun stuff right from the opening shot: A long, uninterrupted take during which each of Earth’s mightiest heroes makes a rousing entrance during a raid on a mountainside compound in an Eastern European country.

Whedon is having a blast here, his camera careening across the battlefield with rib-tickling speed, and this time, you’re able to hop on and take the ride alongside him. When Whedon was given the keys to the first Avengers movie, he had directed only one other film before (Serenity), and his inexperience with juggling all the moving parts of such an enormous enterprise showed. Despite all its commercial and (inexplicable) critical success, the first picture was an impersonal, lugubrious drag, peppered with brief sparks of excitement and imagination.

Age of Ultron is a much more confident work — you can feel Whedon’s artful stamp on every frame — even though it’s bigger in scale and introduces several characters, including the superpowered twins Quicksilver (Aaron Taylor-Johnson), who could beat the Flash in a footrace, and the Scarlet Witch (Elizabeth Olsen), who can mess with the minds of her opponents. They are not the only newbies in the movie, but in an era in which studios reveal way too much of their films in order to ramp up pre-release excitement, there’s no need to ruin here what few surprises the picture has in store.

The big setpieces in Age of Ultron — and there are many — reveal Whedon has become a formidable choreographer of thrilling, furious action. At times, the images resemble panels of a comic book, with careful compositions and visuals (including a fantastic use of a mega-zoom during one of the battles) that don’t feel like more of the same-old. A fight between an angry Hulk (Mark Ruffalo) and Iron Man (Robert Downey Jr.), sporting his Hulkbuster armor, is a showstopper, funny and rousing and imaginative all at the same time. Even more than in the first film, Whedon injects humor into almost every scene, grounding the preposterous goings-on with laughs: At one point, Hawkeye (Jeremy Renner) seems to read the audience’s mind by exclaiming “The city is flying, we’re fighting an army of robots, and I have a bow and arrow!” But to Whedon’s credit, Hawkeye doesn’t come off as outmatched and out of place this time. He holds his own against his much more powerful allies Thor (Chris Hemsworth) or Captain America (Chris Evans).

The plot of Age of Ultron, which is dense only because it builds so much on plot elements from previous films, boils down to a prototypical Big Bad, the sentient robot Ultron (voiced by James Spader), who is also prone to wisecracking and wants to, you know, destroy the world. There is some irony inherent in the story that the villain was an accidental creation of our heroes’ efforts to create a preemptive defense against future invaders from another dimension, but Whedon doesn’t explore that theme too deeply, even though it will figure heavily in the upcoming Captain America: Civil War saga. Age of Ultron does plant the seeds of contention between Tony Stark and Steve Rogers, who don’t always agree on their approach to protecting mankind: For comic fans who know what’s coming, those scenes stand out in a movie that, for the most part, is marking time.

Age of Ultron, which occasionally grazes the cosmic dimensions that the Avengers will encounter in 2018’s Infinity War, still suffers from the inevitable bloat that comes with having almost 10 protagonists. Scarlett Johansson’s Black Widow remains a formidable opponent in a fight, but the movie has no idea what to do with her during the intervals between throwdowns, other than to push her into a half-hearted romance with Bruce Banner that stops the movie and adds needlessly to the 141-minute running time (the issues their subplot raises belong in a different, less frivolous story). Whedon fares better when he keeps his heroes together, such as a scene in which they’re relaxing, knocking back drinks and taking turns trying in vain to lift Thor’s hammer as the buff Asgardian looks on and laughs (only Black Widow declines to try, because she’s a woman and thus the smartest Avenger). Late in the film comes a terrific throwaway gag that pays off the hammer bit with an enormous laugh, a testament to the careful attention to detail Whedon uses as a writer.

Age of Ultron won’t endure the way great genre movies do, because there’s little here worth revisiting. For all its plot convolutions, the story is flimsy and generic, a set-up to much bigger things to come, and the spectacle requires 3D glasses and a giant screen for maximum enjoyment. Watching it at home or on a tablet just won’t be the same. Age of Ultron is a contraption as mechanical as its eponymous villain, but if the film indeed ends up marking Whedon’s exit, he will have left the bar set at an impressive height. Instead of trying to elevate his source material or leaven it with importance, the way Christopher Nolan did with the Dark Knight pictures, Whedon embraces the comics’ pulpy, colorful, playful roots, and he doesn’t try to convert the uninitiated, either (anyone wandering into this movie without a working knowledge of what’s come before will be as lost as someone trying to start on Game of Thrones by watching this week’s episode). Whedon knows this is all nonsense, but it can be great fun, too. Age of Ultron is all rush and sensation with little substance. But what a feeling.

Cast: Robert Downey Jr., Chris Evans, Chris Hemsworth, Scarlett Johansson, Jeremy Renner, Mark Ruffalo, Aaron Taylor-Johnson, Elizabeth Olsen, Paul Bettany, Samuel L. Jackson, Don Cheadle, James Spader (voice only).

Writer-director: Joss Whedon.

A Marvel Studios release. Running time: 141 minutes. Mild vulgar language, comic-book violence, brief gore, adult themes. Playing at area theaters.