Despite some visionary images, the latest DC superhero entry careens through several thinly-conceived ideas.

With the exception of “Wonder Woman” and “The Dark Knight Rises,” every DC movie of the past decade has suffered Marvel Imitation Syndrome. This unique corporate malady takes a successful formula, darkens the frame, and deadens the story, under the assumption that audiences won’t notice. By those standards, James Wan’s “Aquaman” is a cut above: The “Conjuring” filmmaker abandons the witless mess of “Justice League” to craft a colorful, vibrant ocean fantasy, but the considerable effort to improve on a leaden franchise can only float for so long before familiar baggage sinks its potential. Hobbled by a messy screenplay, paper-thin characters, and a hodgepodge of unimaginative showdowns stretched across bloated running time, “Aquaman” is the latest example of a franchise that keeps chasing its competitor’s tail.

Whereas “Justice League” was a feeble attempt to deliver the DC answer to “The Avengers,” Wan’s “Aquaman” imitates Marvel’s “Thor” to an embarrassing degree. Ironically, the half-man, half-aquatic being predates the Norse god in the comic books by some 20 years, but in cinematic terms, this brawny superhero is late to the party. Both movies revolve around a comically muscular man whose attachments to another world complicate his priorities; they both possess evil, power-hungry siblings who force a battle over the rightful heir to their throne, and they’re both forced to contend with a kingdom that works out its problems in a gladiatorial ring. Change a few names and locations in the plot synopsis, and “Aquaman” could have been a “Thor” reboot.” Instead, it’s a maritime riff on the same old song.

Yet “Aquaman” shows glimmers of hope throughout, with visual panache and one of the greatest openings these movies have to offer. The prologue delivers a gothic origin story set on the Maine coast, where a humble lighthouse keeper (Temura Morrison) encounters Atlanna (Nicole Kidman), the princess of Atlantis, washing up on his shore after she’s escaped an arranged marriage in her antiquated underwater kingdom. Once he nurses her back to health, she decides to stick around, and soon they have a newborn child. All is well until Atlantis’ military forces show up, threatening this tranquil seaside union and forcing Atlanna to return home — but not before she unleashes some dizzying martial arts maneuvers against the underwater agents that invade their home. Watching Kidman kick ass for a few minutes makes a good enough case for an Atlanna standalone movie, but “Aquaman” has other priorities.

The couple’s interspecies offspring, Arthur Curry, grows up gradually learning of his abilities: in a fleeting scene from his childhood, his ability to communicate with a shark at the local aquarium deflects human bullies to comedic effect. In later flashbacks, it’s revealed that Atlantean warrior Vulko (Willem Dafoe, collecting a paycheck) trained Arthur to hone his various abilities throughout his youth. Mostly, that means he can swim with gusto, talk underwater, and twirl a pitchfork while making spiffy patterns out of the waves. Wan captures these scenes with a genuine storybook quality, but once Aquaman leaps into action, the story treads water.

The sprawling narrative splits its time between a revenge-prone bad guy dubbed Black Manta (Yahya Abdul-Mateen II) intent on killing Aquaman to avenge his pirate father, and Aquaman’s greedy half-brother, King Orm (Patrick Wilson, blond and glowing with an exuberant fashion sense right out of “Zoolander”). Orm wants to wage a war against humanity for destroying the undersea ecosystem. Unfortunately, the modicum of eco-friendly messaging baked into this motive is muddied by his inane monologues about becoming “Oceanmaster” and a desire to battle Aquaman in Atlantis’ ludicrous “Ring of Fire.”

Arthur’s recruited to stop his sibling by Mera (Amber Heard), the would-be queen of Atlantis who sees a better future in Aquaman’s uncertain hands. The screenplay, credited to David Leslie Johnson-McGoldrick and Will Beall, makes a feeble attempt to transform the instant chemistry between Aquaman and Mera into romcom material, but Heard’s entire performance has been reduced to eye-rolls and smirks to fill in the gaps between various chapters in Aquaman’s journey.

As for Momoa himself, the actor simply lacks the material to turn the character into much more than a heavy metal punchline. Regularly gazing over his shoulder as his flowing hair makes room for his eyes, he looks as though he’s perpetually auditioning for an AXE Body Spray campaign targeting Navy SEALs. The “Thor” movies eventually understood the opportunity to have fun with this kind of virile caricature, but Momoa never becomes much more than a muscular placeholder, and a distorted guitar riff that underscores closeups of his serious stare doesn’t do him any favors.

At times, “Aquaman” contains the hints of a visionary blockbuster: From giant sea creatures swirling through open blue vistas to Dafoe riding a giant hammerhead shark, the film doesn’t lack for ways of transforming the ocean into a delectable universe. But its default mode is paint-by-the-numbers action: By the time King Orm chases Aquaman and Mera out of Atlantis in a giant undersea vehicle, it feels like we’ve been there a dozen times before. One standout bit finds Aquaman and Mera in a late-night battle with reptilian monstrosities in the middle of the ocean, but it comes on the heels of the movie’s worst passage — an inane interlude that places them in Da Vinci Code mode, wandering the Sahara Desert in search of an ancient artifact.

Instead of making one “Aquaman” movie, Wan has made three or four, spinning the wheel and changing modes whenever one idea dries up.

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A lot of “Aquaman” suffers from logic gaps, even on its own slippery terms: How come Mera can breathe oxygen, but other Atlanteans can’t? Why does a normal flare work underwater? How on earth does a gun transform water into beams of “energized plasma”? Audiences keen on pure escapism won’t bother with such distracting quandaries, but they reflect the lack of care for developing a fully realized world. As with much about the DC universe, the whole thing is hobbled by carelessness, which might not hurt box office receipts but certainly doesn’t ensure the long-term appeal of the brand.

Wan clearly put sizable effort into mining a few gratifying moments from the bland rubble of “Justice League.” The cynical, hard-drinking muscleman actually seems like a compelling idea for modern times. As a protector of the Earth’s most fragile environment, he’s the ultimate fearsome rejoinder to the characterization of climate change as a puny liberal ideal. In a better world, “Aquaman” would excel at delivering an ecological message to the masses. But all the fish in the sea can’t salvage a movie that refuses to go more than surface deep.

Grade: C

Warner Bros. will release “Aquaman” nationwide on Friday, December 21.

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