Long before Luc Besson dreamed up the wild but darkly whimsical world of Léon: The Professional, or the madcap space adventure The Fifth Element, the visionary filmmaker was a wide-eyed boy poring over the French science-fiction comic Valérian and Laureline, written by Pierre Christin and illustrated by Jean-Claude Mézières. As Besson began to make movies, the dream of bringing these wild adventures through space and time to the big screen burned deeply in his heart. And now, at long last, after much Instagram teasing and decades of anticipation, the time has come: The world will see Besson's Valerian and the City of a Thousand Planets. It's a momentous occasion for the director and sci-fi fans. It's a shame it's not a momentous movie.

Valerian and the City of a Thousand Planets is a sprawling sci-fi wonder, unveiling scads of curious creatures and enticing environments within its titular location, and beyond. Things begin with the pleading and surreal voice of David Bowie singing out "Space Oddity" as an Earthling space station grows and grows, welcoming incoming vessels and inhabitants from all over the world. Wordlessly, this montage gives way to more extraordinary guests, extraterrestrials who glow, insect-like beasts, hyper-intelligent jellyfish in protective robotic suits, and more line up to awe us, and aid in the construction of Alpha Station, where 30 million lifeforms live in harmony as they spin about space. Within moments, Besson has offered a feast for the eyes and imagination, sure to make sci-fi fans swoon. But he's just getting started.

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Cut to 400 years later and a planet of beaches and sherbet colored skies, where lithe, opalescent humanoids glitter and grin as they go about a regal pearl-collecting ritual. The camera, swirling in this purely CG environment, focuses on a charming princess so full of life and joy she can't help but dance, swinging her slender limbs about in a riveting rhythm. It's a fascinating world so succinctly realized, you may well want to stay, or at least linger for a bit. But the sky falls, and its great trauma thrusts us to the main plot and its heroes, Valerian and Laureline. Regrettably, here is where the film loses its luster.

Following in the tradition of Captain Kirk, Han Solo, or even Star-Lord, special agent Valerian (Dane DeHaan) is introduced as a heart-breaking bad boy, whose thirst for interplanetary adventure cripples his romantic relationships. Still, that doesn't stop him from haranguing Laureline (Suicide Squad's Cara Delevingne), his partner in crime-fighting, about how they should get married. With side-eye and a sharp smirk, she brushes off his advances, arguing he's not ready to commit. But the greater obstacle to their unavoidable romance is the pair's complete lack of chemistry. Whether they're wrestling in bathing suits, hand-in-hand leaping away from the menacing maw of a fanged alien, or battling side-by-side blasters drawn, they have all the sexual heat of a moldy sponge and a hardened glob of chewed gum.

He's reckless, and tenacious in his flirting. She's steely, and relentless in rebuffing him. It's a collision of character repeated ad nauseam, spiked occasionally with professions of love so overwrought they feel more suitable to a Hallmark card than the mouth of an admitted womanizer. Besides this lackluster chemistry and the one-note "opposites attract" dynamic, DeHaan feels wildly miscast. Other characters respond to him as if he's a man's man, a man to be reckoned with, a dashing man of action! But rail-thin, short, pale and with a boyish baby-face, DeHaan is a far cry from Harrison Ford, of even Chris Pratt. He feels too wee, too wan, and most of all too devoid of raw charisma the sci-fi rogue role demands.

As the thin McGuffin plotline spins out to one of conspiracy, cover-up, and intergalactic politics, the movie spirals into the cringing convolution. Still, this might have been saved by a solid slap of star power, greasing the rough spots with a winsome smile, and an enviable confidence, and an indisputable sex appeal. To his credit, DeHaan throws himself full-bodied into the role, but he doesn't have the oomph to carry it off. He's more "aw shucks" than "hot damn." For her part, Delevingne delivers smolder and a bit of swagger. But as most of Laureline's lines are essentially nagging Valerian, she's trapped in a tired stereotype, and so can't right this catastrophic course, either.

As a whole Valerian and the City of a Thousand Planets is an astonishingly ambitious effort, but it's heroes prove its greatest weakness. Nonetheless, this is still a must see for sci-fi fans.

Amid its sloppy story and behind its dud leads, there's a rich and realized world that begs to be seen. There are dreamy beaches of a far-flung planet, an ornate and winding interdimensional market place filled with baubles and beasts, and the skeezy yet sensational red-light district where a LED-lit cowboy/pimp named Jolly (a perfectly cast Ethan Hawke) introduces the scene-stealing sex worker Bubble (a mesmerizing Rihanna). Strutting into the red light and spinning from one fetish costume to the next (cabaret singer to naughty nurse to school girl to French maid), the pop star delivers a string of wow moments, along with Valerian and the City of a Thousand Planets's kinky answer to Fifth Element's Plavalaguna epic opera performance. In moments like this, we can almost forget and forgive the movie its bland romance and uninspiring heroes. Almost.

Valerian and the City of a Thousand Planets premieres at the Fantasia International Film Festival on July 19. A theatrical release follows on July 21.