How is the “Aquaman” movie? A better question might be: How are the “Aquaman” movies? The new action-adventure flick, a stand-alone spinoff of DC Comics’s Justice League franchise centering on the amphibious superhero Arthur Curry (Jason Momoa), doesn’t register as one movie but a myriad.

Some, to put it kindly, are better than others.

The overarching story is kind of poetic, a myth-like fable of a half human, half-Atlantean hero whose very nickname — conferred on him, in this telling, by social media — expresses his dual nature: part landlubber son of a lighthouse keeper (Temuera Morrison), and part sea creature, born to the queen of the underwater kingdom of Atlantis, Atlanna (Nicole Kidman). Part fish, part fella, he’s a man at war with himself, torn between the terrestrial and the marine.

That’s sounds pretty good, right? Except in this busy-to-the-point-of-baroque blowfish of a movie, the titular protagonist is not really at war with himself but with a host of other external adversaries. At times, the plot feels like the 12 Labors of Hercules, with a couple of extra labors thrown in just for the heck of it.

There are two main villains. The first (and most straightforward) one we meet is a high-tech pirate (Yahya Abdul-Mateen II), a man whose early defeat by Arthur/Aquaman — and the collateral death of the pirate’s father (Michael Beach) — drives him to become the cartoonish evildoer Manta, a bad guy in a bug suit with one thing on his mind: vengeance. The second antagonist has even more issues. He’s Arthur’s jealous half brother Orm (Patrick Wilson), the son of Atlanna and her royal consort Orvax, and the betrothed of Mera (Amber Heard), a Xebelian mermaid — with two legs instead of a tail, and an iridescent cat(fish)suit — who eventually leaves Orm and becomes Arthur’s squeeze. That romantic sidestory, which at times plays out like a silly, meet-cute romcom, is actually sort of entertaining, although Heard, outmatched by the screen presence of her charismatic co-star, feels like a fish out of water.

But it’s exhausting just to write all that, and we haven’t even dived below the surface of this 20,000-league-deep (yet surprisingly shallow) saga. Imagine having to sit through the movie, which, at 139 minutes, is about 45 minutes, and five extraneous subplots, too long.

Here are a few of them: Orm wants to wage war on the humans for their pollution of the seas with trash and warships. To do so, he must defeat or persuade the other undersea kingdoms. To stop him, Arthur is tasked with finding his ancestral power-weapon, a search that will lead him and Mera on a journey to the Sahara desert, a Mediterranean village, the lair of a scary talking sea monster (voiced by Julie Andrews) and various other submarine locales, all the while pursued by Orm, Atlantean stormtroopers and Manta, who is now armed with a weapon that converts water into beams of “energized plasma.” (In other words, it’s a squirt gun.)

There are also flashbacks to the teenage Arthur (Kekoa Kekumano) receiving martial-arts training from the Atlantean courtier Vulko (Willem Dafoe).

To recap: “Aquaman” is an eco-conscious superhero origin story that at times is reminiscent of “Clash of the (Sopping Wet) Titans,” “Romancing the Stone,” a couple of Japanese monster movies and “The Sword in the Stone.” Am I forgetting anything? Probably. It’s also wildly in violation of nearly every law of physics, even by the loose standards of super­hero movies, not to mention dizzyingly confusing for viewers not steeped in DC Comics lore. Take your resident nerd friend, if you have one, as backup. Otherwise, be prepared to Google the heck out of this movie.

On the plus side is the eye-popping production design, although that is also, like the plot, too, too much, dazzling the eye with more fantastical Atlantean technology and — inexplicably — underwater fire than a Las Vegas edition of Cirque du Soleil. Like the frequently shirtless Momoa, it’s pretty at first, then it just hurts.

PG-13. At area theaters. Contains sequences of sci-fi violence, action and some strong language. 139 minutes.