Based on Pierre Christin and Jean-Claude Mézières' 1967 French comic series "Valérian and Laureline," $180-million fantasy epic "Valerian and the City of a Thousand Planets" has been a longtime passion project for writer-director Luc Besson (2014's "Lucy"). The film is overflowing with extravagant places and sights never before seen on film, populated by otherworldly creatures born from the boundaries of one's imagination. By all intents and purposes, it should be a monumental cinematic experience of excitement, wonder and romanticism. Instead, it just kind of sits there, seldom kicking into high gear. Lugubrious when it should be thrilling, wooden where it should be swoon-worthy, and reliant on a punishing swath of exposition at precisely the moment when it ought to be embracing the visual razzmatazz of it all, "Valerian and the City of a Thousand Planets" is ultimately not half as fun as it wants to be.

David Bowie's ethereal rock classic "Space Oddity" is the stirring entry point into a story that never again captures the magic of its opening-credits montage, a dizzying snapshot of Earth's history of space exploration through the ages. Picking back up in the 26th century, flirtatiously sparring federal agents Valerian (Dane DeHaan) and Laureline (Cara Delevingne) zoom from one intergalactic mission to the next while dreaming of a restful beach vacation. First, they are tasked with saving the "thousand planet" city of Alpha from a deadly, fast-growing contamination threat while retrieving a mysterious converter and a precious pearl, surviving remnants of the destroyed utopian planet of Mül.

"Valerian and the City of a Thousand Planets" is nothing if not a smorgasbord for the eyes. Despite Besson's overload embrace of CGI ranging from the dazzling to the cartoonish, this is a kaleidoscopic wonderland of a film—albeit, one which manages to feel bloated at its current 137-minute length but takes little time to capture the crucial wondrousness of its surroundings. The narrative proper falls into repetition as Valerian and Laureline take turns getting into hot water and rescuing each other for the duration. Action sequences frequently shift into first-person video game mode as characters pummel through walls and leap across cliffs without trepidation or even the slightest concern for human fallibility. One chase sequence set in the "Big Market" of Planet Kyrian—a desert wasteland transforming into a bountiful new world with the wearing of a special helmet—is compromised by the tacky, bluish holographic effect placed over Valerian and the other visitors that makes them look like ghosts from Peter Jackson's 1996 horror-comedy "The Frighteners."

Valerian's visit to Alpha's red light district of Paradise Alley leads him to shape-shifting cabaret dancer Bubble (Rihanna), her sizzling introduction marking a temporarily hopeful turning point as energy and momentum finally spark to life. Rihanna's (2012's "Battleship") acrobatic choreographed performance, blending seamlessly with a roundelay of costume and hairstyle changes, is a dynamic showstopper. For the roughly twenty minutes she is onscreen, agreeing to assist our heroes in hopes of finally winning her freedom, the film captures the one-part fleet-footed, one-part high-spirited, one-part touching tone it should have had all along.

Had a more dynamic pairing been front and center, perhaps Valerian and Laureline's love story would have felt less cloying and their interchanges more convincing. Dane DeHaan (2017's "A Cure for Wellness") has proven to be a tremendous talent, and he is as eye-catching as usual here. Alas, Cara Delevingne (2016's "Suicide Squad") too often appears stilted and uncomfortable, her monotone deliveries sapping away whatever chemistry she may have shared with DeHaan. Watching the film, it was impossible not to wonder how much livelier and impassioned the proceedings might have been with a more confident actor—Emma Stone repeatedly came to mind—embodying the headstrong, quick-thinking Laureline.

In a film of so much muchness, one would presume there would be a lot to discuss and debate. As overstuffed with characters and plot points as it is, however, "Valerian and the City of a Thousand Planets" has surprisingly few layers. With the exception of a playful, gender-based power struggle between Valerian and Laureline, what is glimpsed on the surface is pretty much all there is. Boundless 2012 sci-fi masterpiece "Cloud Atlas," this is regrettably not. Fortunately, it's also not 2015's "Jupiter Ascending," Lilly and Lana Wachowski's clanking mini-fiasco of a follow-up. "Valerian and the City of a Thousand Planets" is too ambitious and valiantly conceived to write off completely, but it's missing an all-important beating heart at its center. Giving one little to think or care about, it straddles in limbo between almost spectacular and a lamentable missed opportunity.