The biggest battle in "Avengers: Age of Ultron" — which is a movie of many, many battles — is the one between writer-director Joss Whedon and the massed forces of Marvel Studios. Whedon strives to enrich the film with the sort of crackling wit and soulful character sidelights for which he's noted. But you can almost hear his Marvel overlords (and Marvel's own Disney overlords) objecting throughout, demanding more noise, more chaos, more budget-justifying digital effects. Whedon, who has wearily announced he won't be back for the next "Avengers" sequel, was overmatched.

He put up a good fight, though, and the movie's best stretches are clearly his. Sly lines of dialogue glimmer by like fireflies. ("I totally support your avenging," says one character's newly revealed spouse.) And there are low-impact scenes — such as the one in which two Avengers quietly flirt over ruby-red cocktails in some kind of superhero nightclub — that open up the characters and make us care about them. But then Iron Man suits up and Hulk goes code-green, and the tumult resumes (collapsing buildings, careening transport, the usual). By the time the movie hits the two-hour mark — with 20 minutes left to go — we're numb with CGI overload.

The story, distilled by Whedon from decades' worth of comic-book tales, is fun pulp. The basic gang is back: wisecracking Tony Stark/Iron Man (Robert Downey Jr.), lethal Natasha Romanoff/Black Widow (Scarlett Johansson), straight-shooting Steve Rogers/Captain America (Chris Evans), sad-inside Bruce Banner/Incredible Hulk (Mark Ruffalo), arrow master Clint Barton/Hawkeye (Jeremy Renner) and hammer-hurling Norse god Thor (Chris Hemsworth). Former S.H.I.E.L.D. chief Nick Fury (Samuel L. Jackson) nibbles around the edges of the plot, and semi-superguys War Machine (Don Cheadle) and Falcon (Anthony Mackie) fly in from earlier "Iron Man" and "Captain America" films. There are newbies, too. It's a crowded picture.

The Avengers once again have a lot on their hands. Loki's glowing scepter (now Loki-less) is back in play. There's a troublesome African gunrunner (Andy Serkis), and there's a pressing need for the exotic substance called vibranium. Faint clackings of the legendary Infinity Stones are also audible. In addition, the Hydra terror org is still around and has been brewing up "enhanced" humans in its dismal European lair. Chief among these beings are the spooky Maximoff twins, Wanda (Elizabeth Olsen) and Pietro (Aaron Taylor-Johnson). Wanda has the power to cloud minds with nightmares, and Pietro can zoom around at blur speed. ("He's fast, and she's weird," as one character helpfully shorthands it.) Both twins hate Tony Stark (his company's munitions killed their parents) and, by extension, his fellow Avengers.

Unaware of this new threat, Stark is at his New York headquarters creating an artificial intelligence so formidable in its powers that Tony believes it can be used to impose upon the world "peace in our time." (He's unconcerned about how that might be done.) He names this entity Ultron (incarnated by James Spader), and before long, it has taken on a towering metal-man form. Here we have a small breakthrough in movie robotics. Whereas most such creatures have usually been constricted by their deadpan mechanical mugs, Ultron has a cleverly articulated face, which allows him to project wry attitudes (amusement and disdain, for the most part). He also has an amusing way with a one-liner. ("I wanted to take this time to explain my evil plan.")

Squadrons of other robots wade into the picture from time to time, and what with the globe-girdling glut of international locations (Johannesburg and Seoul, with layovers in Italy, England and Bangladesh), confusion is always near at hand. Fortunately, Whedon has written at least one good scene for each of the Avengers, with attendant illuminating discourse. (Super-archer Hawkeye expresses the reservation I've always had about his character when he says, "We're fighting an army of robots, and I have a bow and arrow.") Most striking is an elegiac scene at the end — involving two contending super-characters — which has an emotional pull rarely felt in this sort of big-bucks blockbuster.

Whedon has said he wanted to make "Age of Ultron" a shorter, more intimate film than his first "Avengers" movie. Marvel overruled that plan, apparently. This picture, like its estimable predecessor, goes on too long, and its more probing narrative is crushed by landslides of digital mayhem (which, by this point in megaplex history, is basically high-tech cartoonery). Though not so freshly impressive as its predecessor, "Ultron" is still an entertaining superhero picture. But with two Whedon-less "Avengers" sequels in the works and further adventures of Captain America and Thor on the way, this stalwart crew may eventually be ready for a brief bit of R & R.

Kurt Loder is the film critic for Reason Online. To find out more about Kurt Loder and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com.