There is nothing more difficult for a film critic to write about than a mediocre movie. Great stuff we can enthuse about, terrible stuff we can deconstruct and diagnose, but the very average of cinema just sits there. There is precious little to praise, and there is little to point out that is so specifically wrong-headed that it deserves comment. It is simply ordinary.

Here comes Craig Gillespie’s Supergirl, huffing and wheezing like a middle-aged man trying to prove he is ‘down with the kids’. It is the second feature film of Warner Bros’ shared universe of DC Comics adaptations, following last year’s surprising and overloaded Superman. While less insanely packed with characters and content, this new film fails to replace it with anything of note. What fails to work is simply dull. What does stand out largely feels ripped off from someplace else.

In James Gunn’s Superman there was a delightful scene where its protagonist argued that he was a little – in his words – ‘punk rock’. The scene worked so well because not only was Superman hilariously off-base but it absolutely pinpointed the core of his appeal. He is what is often called “the big blue boy scout’: idealistic, overly polite, and the sort of anti-Batman one could comfortably take home to meet one’s mother. DC Comics more broadly is bright where Marvel is dark, silly where Marvel is often serious, and entirely unafraid of mockery. It is what, for me, made Gunn’s relaunch such a delight. It brought to mind a line once written by comic book superstar Grant Morrison about the Justice League of America: “Great name, guys. Does what it says on the tin, and isn’t afraid to be laughed at.”

Gillespie’s take on Supergirl, written by Ana Nogueira and inspired by the comic book Woman of Tomorrow, tries to make out Kara Zor-El (Millie Alcock) actually is punk rock. Traumatised by the death of her parents and the destruction of the planet Krypton, she flies a spaceship from one planet to another getting blind drunk and resisting any sort of call to adventure. We know that she is a cynical person because she keeps telling people how cynical she is. We know that she is edgier than other superheroes because she staggers around in a shabby overcoat instead of her famous costume.

Kara’s path intersects with that of Ruthye (Eve Ridley), orphaned daughter of a master swordmaker, now hunting down the warlord that killed her parents to execute him with her father’s final blade. An encounter with that warlord, the slave trader Krem (Matthias Schoenaerts), sees Kara’s dog Krypto shot with a poison dart and sends Kara after Krem – Ruthye in tow – to find an antidote and get revenge.

You can tell Krem is punk rock, since he bears a mass of facial piercings and looks as if he has walked off the set of one of George Miller’s Mad Max sequels. Facial piercings, like tattoos, really do not carry the cultural weight that they used to. Without any other distinctive or memorable features, Krem is the sort of off-brand villain one buys from K-Mart.

There is an extent to which one can see Supergirl as a science fiction remake of Henry Hathaway’s 1969 western True Grit: the earnest girl hiring the over-the-hill, miserable cowboy to help get revenge against the evil bandit. Of course Hathaway had the American west as a visual backdrop, while Gillespie resorts to a series of increasingly brown and drab CGI planets. There is so much potential in this sort of science fiction adventure for eye-popping visuals and colourful set pieces. James Gunn clearly understood this with his three Guardians of the Galaxy films for Marvel Studios, and Gillespie’s film is palpably taking inspiration from that trilogy here, so the fact that everything looks so dull as miserable must be the result of a purposeful, misguided attempt to look dark and mean. After all, this is Supergirl: so punk rock.

One assumes this push to be so mean and dour is what influenced the bizarre decision to use Krypto – the delightfully chaotic super-powered dog from Superman – as a motivator for Kara rather than a character in his own right. It leaves one of the film’s most delightful assets off the game board, and weirdly makes a whole part of the narrative about a cute animal suffering.

Weirdly one thing that Supergirl does resemble is the discontinued DC Extended Universe of 2013 to 2023, which was largely overseen by director Zack Snyder and which indulged in a particularly bleak and violent take of DC’s typically more upbeat roster of heroes. Snyder’s more ardent fans have been complaining ever since things were rebooted. If they continue complaining about this film, then you know they were never genuine.

Millie Alcock, it must said, is great, and absolutely excels in building a distinctive and entertaining variation of Supergirl that sits far apart from the more traditional Superman Jr versions typified by Helen Slater (1984) and Melissa Benoist (2015). Another performance of note is from Jason Momoa, playing the alien bounty hunter Lobo. The character is a cult figure in DC Comics, and this film’s one major concession to a broader DC Universe, and Momoa is clearly having a wonderful time playing him. He is well utilised too, with a solid understanding that a little Lobo goes a long way.

Alcock has already been confirmed for next year’s Superman sequel Man of Tomorrow, and her character is a strong addition to DC Studio’s burgeoning franchise. This film, however, is simply by-the-numbers product. There is none of the freewheeling chaos of Gunn’s Superman, nor the smart writing of Tom King’s Woman of Tomorrow comic – from which Supergirl ostensibly takes its lead. There is nothing specifically bad on display, but its audience is unlikely to remember much of it by the time the next DC Studios production comes around.