“Avengers: Age of Ultron,” Reviewed: Superheroics and String Theory.

Chris Evans and Chris Hemsworth in 'Avengers: Age of Ultron.' (Marvel/Disney)

Chris Evans and Chris Hemsworth in ‘Avengers: Age of Ultron.’ (Marvel/Disney)

Photoshop, the image-manipulation software NASA used to fake the moon landing, has a useful feature called Flatten Image. After you’ve monkeyed around with backgrounds, foregrounds, colors and shading, flattening the file seals those changes into a single impenetrable level – as if putting the image behind glass, or, I suppose, turning it back into a unchangeable photograph. (At least, I think that’s how it works. I hardly ever use Photoshop.)

For some reason that particular analogy popped into my head last night during a screening of Avengers: Age of Ultron (rated PG-13) – and it wasn’t because I watched it in 2D instead of 3D. Writer-director Joss Whedon, the reigning creative king of the Marvel Cinematic Universe, has pulled off the impossible and delivered a skillful sequel to his 2012 ensemble opus that’s bigger, louder, more complex and yet easier to follow than the first Avengers. By rights there should be too many characters in this film, and yet no one feels shortchanged by the brisk plot and adorably chatty script. (Don’t get too attached to each and every character, however: This is still a Whedon movie, if you know what I mean.)

And yet there’s this … flatness to the affair. It’s a product that feels like a product – processed, spliced and diced, and pre-chewed for easy digestion. Age of Ultron is absolutely entertaining, but that inescapable feeling of manufactured-ness keeps the puppet, as it were, from becoming a real boy.

The first Avengers was obligated to spend precious minutes bringing the superheroic band together, but this sequel quite literally hits the ground running. There’s an opening sequence that’s wall-to-wall action, as our team of heroes – Captain America (Chris Evans), Iron Man (Robert Downey, Jr.), Black Widow (Scarlett Johansson), Thor (Chris Hemsworth), Hulk (Mark Ruffalo) and Hawkeye (Jeremy Renner) – beats the snot out of a platoon of rent-a-goons in an eastern European forest. There they find Loki’s scepter, lost since the first film, as well as a super-powered brother-and-sister team, Pietro and Wanda Maximoff (Aaron Taylor-Johnson and Elizabeth Olsen, looking much less married than they did in last summer’s Godzilla), with an axe to grind against Downey’s Tony Stark.

Downey remains the MVP of the MCU, giving us a wisecracking Iron Man whose brilliant mind is both his secret weapon and his own worst enemy: Stark thinks too many levels ahead, and lets his anxieties about what could happen color his actions in the moment. In this case, the futuristic energy contained in Loki’s scepter inspires him to create that artificial intelligence he’s been dreaming of – he’s worried about threats that might someday be bigger than the Avengers can handle, and as an inventor he figures he can build a machine that will save the day.

It doesn’t work. That AI is the robotic Ultron (James Spader), and literally within the time it takes for the Avengers to enjoy an after-hours party, this newly created super-intelligence calculates that the best way to protect humanity is to wipe it out – starting with our heroes. Ultron is connected to the world’s computers and likes to create increasingly indestructible bodies for himself to inhabit; he’s a tough cookie. And when the other Avengers learn who created him, they get sooooo mad.

Age of Ultron hits its marks with deceptive ease: The battle sequences are long and sustained and (mostly) well-choreographed, and a couple of times Whedon cuts to slow-motion to let us drink in the full-tilt glory of an orgiastic scene of wide-scale super action. He’s still at his best, though, in the human moments between the characters – the running jokes about Cap’s fuddy-duddies and Thor’s enchanted hammer, and a surprisingly sincere flirtation between Johansson’s emotionally scarred former killer and Ruffalo’s scientist who fears the gamma-generated rage machine that lurks inside him.

After 11 interconnected films we know what to expect from the MCU brand in general, and Avengers in particular: Each film exists to thrill us in the moment and prepare us for the next chapter. On that score Age of Ultron is pretty close to an unqualified success … but I’m not surprised to learn that Whedon himself has said he’s done with the franchise after this entry. He’s a pop-culture geek, but his own superpower is his ability to inject humanity into his creations. At one point Ultron references Pinocchio, as I did above, and comments that there are no strings on him any more. But the film’s strings are still there, and the bigger the MCU gets, the harder it will be to ignore them.