Eurotrash on steroids as only Luc Besson can confect it, “Valerian and the City of a Thousand Planets” is a goofy special-effects acid trip in the form of a berserk science-fiction cartoon. Attempting to replicate the weird popularity that “The Fifth Element” enjoyed two decades ago, Besson has seized on an old comic book by Pierre Christin and Jean-Claude Mézières—for inspiration and lavished upon his adaptation a cornucopia of blazing colors, digital creatures alternately benign, threatening and just plain odd, heroic derring-do and “Cabaret”-style sensuality. The result is an opulent but incoherent mess that fails to provide the loopy entertainment it promises.

The plot isn’t what you’d call cerebral. After a prologue swiftly covering the history of human space exploration, man’s encounters with extraterrestrials and the launching of a space station called Alpha that grows like Topsy and is eventually launched deep into the universe by none other than Rutger Hauer in a tiny cameo, the film switches to a planet called Mül, where a sleek, shimmering alien race live an idyllic existence marked by collecting pearls from the azure sea and then returning one, multiplied by a cute little animal who consumes it and then produces an avalanche of them, into a well as a sacrifice to the gods. Unfortunately, the bliss is brutally broken by an attack of monstrous spaceships. Some of the aliens escape in a ship of their own, but their princess does not reach it in time.

The whole episode, we next learn, is apparently a nightmare experienced by Valerian (Dane DeHaan), who is supposed to be a top agent in the United Human Federation headquartered on Alpha, which has grown into the megalopolis of the title, housing a myriad of species. Major Valerian and his partner, pretty Sergeant Laureline (Care Delevingne), are given a special assignment by snarling Commander Arun Filitt (Clive Owen): they must crash into a heavily-fortified compound called Big Market and steal a priceless converter being auctioned off by a Jabba the Hutt-like crime boss called Igon Siruss (voiced by John Goodman). After some frantically pointless action they succeed, and wouldn’t you know the converter turns out to be that cute little critter from Mül? They also get their hands on one of those precious pearls from that planet.

From this point the scenario gets crazier and crazier. Leftover Mül aliens show up and attack Federation headquarters, sending Valerian and Laureline into a series of adventures marked by flamboyant visuals (including a passel of huge, hungry thingies that resemble the goofy alien from Joe Dante’s “Explorers” and a shape-shifting dancer named Bubbles, played by Rihanna, who works in a semi-brothel run by a character called Jolly the Pimp, played by Ethan Hawke). The cacophony is ultimately resolved by the connection of all the present mayhem to the long-ago destruction of Mül, and Valerian and Laureline learn why all information on that planet has either been erased from Federation records or consigned deep into top secret territory. Of course, they set things right.

Much of your reaction to the lunacy of “Valerian” will depend on how you respond to its menu of visual excess—the vibrant, cotton-candy colors, multitudinous CGI creatures and an avalanche of spectacularly extravagant (or, if you’re in the wrong mood, indescribably ugly) backgrounds. It’s a cinematic head trip of the sort that attracted stoners to the front rows of “2001: A Space Odyssey” back in the late sixties—particularly with 3D added to the mix. But Kubrick’s film had ideas behind the surface; Besson’s doesn’t. It’s simply an empty exercise in self-indulgent flash.

Still, that wouldn’t be fatal if it weren’t also burdened with horrible acting by the humans on hand. The ordinarily reliable Owen snarls and screams like a B-movie villain; it’s probably his worst performance ever. Hawke is even more grotesquely over-the-top, and though Rihanna looks fine, she obviously needs more help from a director that she receives in this case. Delevingne is certainly attractive too, but apart from a weird sequence with those “Explorers”-like critters, she offers little beyond a stern expression. As it is, though, she’s far preferable to DeHaan, who is utterly miscast as Valerian. The character is supposed to be a swashbuckling he-man, but DeHaan looks like a scrawny fourteen-year old trying to act like Han Solo, but a dissolute one with huge bags under his eyes. He barely manages the sword-swinging moments and even seems uncomfortable in the “deep” moments when Valerian is torn between his duty to the Federation and doing the moral thing.

While DeHaan flounders throughout, however, it’s really not his fault that the long stretches of supposedly romantic banter he conducts with Delevingne fall so terribly flat. True, it’s hard to stomach his pathetic efforts at preening masculinity, but the real fault lies in the atrocious dialogue Besson has provided him with—lines that would have sounded flat and clichéd even in a bad screwball comedy from the 1930s. In the past Besson has relied on others to “fix” his English scripts so they’d sound less clumsy and banal, but here he seems to have foregone that step in the writing process, with disastrous results. The romantic stuff is the worst, but the rest of the dialogue isn’t much better.

Of course, neither writing nor acting is the raison d’être for a movie like this. The first “Star Wars” episode was hardly notable for either, but it was both surprising and exhilarating. “Valerian” is neither. It resembles nothing so much as one of those horrible attempts to mimic Lucas’ picture that proliferated in the eighties, which were also crammed with gonzo effects and dumb ideas. It’s said that the fate of Besson’s studio Europa, which has suffered a string of box-office disasters since its inception, depends on the success of this mega-budget misfire. Well, studios have shut down before. Adios.