Beware the movie that's Fun! with a capital F, the one populated with seemingly unpretentious characters who say adorable, clever things, the one that presents each off-kilter joke as if it were a porcelain curio, the one that boasts a comfort-food soundtrack of songs you've always liked but perhaps haven't heard in a while. On the plus side, James Gunn's Guardians of the Galaxy, adapted from the Marvel comic book series of the same name, has a sense of humor about itself: Even when characters strut around dropping hefty expository bundles such as “Ronan is destroying Xanderian outposts throughout the galaxy!” they do so with a wink. But by the end, you'll have been winked at so much you may think you've been staring at a strobe light for nearly two hours. Guardians of the Galaxy is proof that a picture can have a sense of humor yet have no real wit. It hits every beat, but it hasn't got the beat.

CGI-created characters Rocket and Groot are the most naturalistic element of Guardians of the Galaxy.

You might be fooled into thinking otherwise at the beginning. Guardians opens with a flashback preamble detailing a key episode in the childhood of our hero, Peter Quill (played, as a youngster, by Wyatt Oleff): His mother, dying in a hospital, begs him to take her hand; he recoils, only to be filled with remorse seconds later when she draws her last breath.

The totem he clings to is a mixtape of “Awesome Music” she's made for him, filled with rad-pop treasures from her own youth and maybe from yours, too, such as the Raspberries' “Go All the Way” and 10cc's “I'm Not in Love.”

Cut to Quill as a brawny, space-roaming grown-up, now played by Chris Pratt: He's still listening to that tape, and we see him, headphones clamped to his ears, swaggering through a dazzling, surreal, blue-green alien landscape — rife with obnoxious, scampering lizards, which he impatiently kicks out of the way — to the strains of Redbone's “Come and Get Your Love.”

Fun! Right? Actually, that early sequence almost is fun, though it's just a little too self-aware, too pleased with itself, to work. Later, rogue space scavenger Quill is joined in his exploits by green-skinned butt-kicker Gamora (Zoe Saldana), beefcake-y, tattooed chrome-dome Drax (pro wrestler Dave Bautista), and an unlikely duo of soldiers of fortune: cranky, talking raccoon Rocket (voiced by Bradley Cooper) and his bark-covered sidekick, Groot (Vin Diesel), a thinking, feeling, ambulatory plant form with exceedingly sad, slightly watery eyes.

Naturally, none of these characters likes one another much at first. But they quickly realize that five heads and 12 legs are the bare minimum needed to prevent the villainous, stripey-face Ronan (Lee Pace) from destroying the galaxy. Also, at one point they'll have to take a meeting with Glenn Close and her winter-white pretzel hairdo, and that's seriously scary.

Gunn has to juggle so many plot elements in Guardians of the Galaxy — so many booming galactic battles, so many whisker-close brushes with death, so many almost-poignant moments of epiphany — that it's little wonder he loses his grip on the thing. Then again, he and Nicole Perlman wrote the script (adapting it from the comic books by Dan Abnett and Andy Lanning), so they bear some responsibility for its top-heaviness. Gunn inserts occasional moments of wonder — in the most effective one, a character makes a sacrificial act to save the others, as twinkling lights, ostensibly representing compassion and generosity, dot the frame. But he doesn't bother to smooth over the seams. Time and again, he cues us what to feel, which is different from creating the perfect weather conditions for it and then stepping back.

What really kills the fun — as opposed to the Fun! — of Guardians of the Galaxy is its desperation to be casual and quirky and irreverent nearly every minute. Groot and Rocket are, admittedly, well designed: Rocket, with his expressively raggedy fur, comes off as a crotchety refugee from Fantastic Mr. Fox. And the perpetually sorrowful Groot, his arms and legs a tangle of art nouveau roots, strikes the right balance between somber elegance and whimsy. (Diesel makes the most of the single growly line Groot repeats throughout the movie — “I'm Groot!” — turning it into a lament or a declaration, as needed.)

Oddly enough, these CGI-created characters are the most naturalistic element of Guardians of the Galaxy.

Otherwise, the movie works so hard to advertise its disreputability that it comes off as anything but. At one point, Quill not-so-subtly flips the bird to an intergalactic cop, putting an old schoolboy's trick to use. Pratt — an actor with a degree of rakish charm — feigns innocence at his own naughtiness, and the moment is almost funny. But though Quill is, ostensibly, a lady killer who swears like a sailor on shore leave, he's repeatedly forced to use the distractingly demure term “a-hole.” The saltier, full-strength version would give offense to the dark lords of the MPAA, who would, in their wrath, snatch away his movie's PG-13 rating. It's all just too precious for words. Especially those four-letter ones.

GUARDIANS OF THE GALAXY | Directed by James Gunn | Written by Gunn and Nicole Perlman | Walt Disney Studios Motion Pictures | Citywide

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