Last summer’s reboot of “Superman” was a movie that provoked reactions all over the map. Some liked it, some didn’t, but even if (like me) you were in the positive camp, the movie was trying to be so many things at once that your appreciation for how close it came to echoing the vibe and style of comic books might have scraped up against your feeling that it was all a bit…busy. That said, there was one thing about “Superman” that perhaps the whole world could agree on: In that 12-minute-long argument between Clark Kent and Lois Lane (mostly a very good scene), the moment when Clark made the case that Superman’s wholesome valor was “punk rock”… well, that was cringe. The second you call anything “punk rock,” it has ceased, in that moment, to be “punk rock.” (It has instead become lame.) And Superman calling what he does “punk rock” is super-cringe.

In that light, here’s the key thing to know about “Supergirl,” the second outing from James Gunn’s DC Studios: The entire movie thinks it’s “punk rock.” It opens with Krypto the superdog peeing on a newspaper headline about Superman saving a small town. From there, the film introduces us to Kara Zor-El (Milly Alcock), who rather than being the spunky Supergirl of legend, saving earthly lives in a primary-colored spandex suit, is an interplanetary drunk in a Blondie T-shirt (how punk rock!), bopping from one arid dystopia to the next, seeking out junk-heap bars on junk-heap planets, getting into fights set to razory anthems by Wet Leg and Halsey. The villain, Krem of the Yellow Hills, is an overly derivative “Mad Max” reject, played by the Belgian actor Matthias Schoenaerts with a shaved head and scraggly ponytail and rows of silver pellets piercing his face and an accent that might be from Transylvania — think the Lord Humungus meets Pinhead meets Adam Sandler. We’re told that Krem, a human trafficker who leads a group of space pirates known as the Brigands, possesses the strength of 10,000 men. But we’d be happier if he had the magnetism of one interesting one.    

The Australian actress Milly Alcock is 26, but as Kara she has the look and aura of someone younger, with a touch of wild-child ’70s androgyny. She’s like Kristy McNichol crossed with the Feral Kid from “The Road Warrior” in oversize Penny Lane sunglasses. Alcock is likable enough (underneath it all, she often seems like Little Orphan Annie with desert-wastrel hair), but the character as written is so one-note that it’s hard to have much investment in what she’s up to.

Of course, maybe that’s because the movie has no story! As Kara plays hooky from her life on Earth (just because), we see Krem commit a pair of brutish actions that set off what passes for the plot of “Supergirl.” The beloved terrier Krypto gets shot with a poison dart that will kill him in 72 hours; that’s how long Kara has to retrieve the antidote. And then there’s the matter of Ruthye Marye Knoll (these names! Are they trying to make the “Star Wars” prequel monikers look elegant?), who watches Krem slaughter her entire family, starting with her father, who’s an artisan of weapons. She’s able to salvage one of his swords (an artifact that feels very sub-“Lord of the Rings”), and she now has one agenda: to get her revenge by killing Krem. We know that because Eve Ridley, as Ruthye, never stops declaiming this goal or deviating from her tone of stoic petulance.

Kill Krem! Save the dog! Those are the motivations driving the entire not-even-interesting-enough-to-be-convoluted plot of “Supergirl.” Maybe that’s why the movie is full of action yet numbingly flat.

Kara has a backstory, which turns out to be an overinflated CGI bummer. Superman’s version of my-home-turned-into-the-apocalypse was at least short and sweet: His planet was getting ready to blow up, so his father, Jor-El, stowed him as an infant into a spaceship, and it landed on Earth. All very clean and mythological. But Kara, who is Superman’s cousin (she’s the daughter of Jor-El’s brother, Zor-El), was born eight years after Krpyton began to implode. The punk-rock dystopia surrounded her from the outset. So by the time she’s packed into a spaceship, she’s losing the family she loves. All of which could have made her a comic-book heroine with a haunted underside, if the move had a haunted underside.

James Gunn, along with Peter Safran, knew that he was launching DC Studios right into the teeth of superhero fatigue. Gunn got asked a lot about how he was going to avoid that, and the key thing he said was: We’re not going into production on any movie until the script we have is rock-solid. For that was the overriding problem with the superhero overkill era: The films had lousy scripts, which were used as grids on which to layer the visual effects. Gunn was right to want to take the comic-book genre back to well-structured screenwriting basics. So what has he done in his second DC outing? He’s given us a comic-book movie with the worst script I can remember. (It’s by Ana Nogueria.)

I’ve never bought the idea that movies were ruined by “Jaws” and “Star Wars,” but watching “Supergirl” you might well think that they were ruined by the Mos Aisley Cantina scene of “Star Wars.” Because that seems to be the movie’s dominant influence. One set piece after another features rubbery creatures with heads like melting anvils and tentacles coming out of strange places, as if this, after 50 years, was still charming and awesome. (Industrial Light & Magic is one of the film’s visual-effects houses.) Actually, the cantina scene was corny even back then, and creatures like these now make you feel trapped in a Muppet movie.

“Supergirl” plods along, poised between sodden spectacle and snark. Jason Momoa shows up as Lobo, a stogie-sucking bounty-hunter biker who’s groomed like a lost member of Kiss, and he gives the film a jolt of untidy energy. David Corenswet pops up for a few scenes as Superman, and that’s enough to make you wish that it wouldn’t take the whole damn movie for Kara to accept her Supergirl identity. “He sees the good in everyone,” she says of her super-cousin, “and I see the truth.” Dark! I was shocked to see that the director, Craig Gillespie, who made the arresting “I, Tonya” and the fabulous “Cruella,” could churn out a piece of product this generic in its action and its attitudinizing. What happened to his barbed humanistic wit? Maybe Gillespie, who’s Australian, convinced himself that the “Mad Max” Lite trappings of “Supergirl” make it a subversion of the genre. It’s all so desperate to be “punk rock.” But “Supergirl” is a punk crock.