“Guardians of the Galaxy” opens Friday at Point, Eastgate, Star Cinema and Sundance. PG-13, 2:02, three stars out of four.

A guy, a girl, a wrestler, a raccoon and a tree walk into a bar . . .

The punch line is “Guardians of the Galaxy,” which injects a much needed adrenaline shot of silliness into the summer blockbuster formula. Using a team of Marvel backbenchers and directed by Jason Gunn, who completely subverted the superhero film in “Super,” “Guardians’ isn’t quite the anti-Marvel Marvel film some folks were hoping for. It uses the same formula and beats as “The Avengers” or “Thor” — it just seems to have a lot more fun with them.

The film opens with a “Raiders of the Lost Ark” homage, as intergalactic thief Peter Quill (Chris Pratt) tries to heist a mysterious orb from a forbidden planet. Sounds like every other Marvel film, except that Peterl is listening to ’70s classic rock on his Walkman while he’s doing it. He’s a child of the ’80s, plucked from earth by a gang of no-good thieves, and his only connection to Earth is the mixtape (“Awesome Mix Vol. 1”) his terminally ill mother made him.

Gunn has a great time pairing the usual dazzling visual effects expected of a Marvel IMAX 3D film with those awesome hits, including Rupert Holmes “Escape (“The Pina Colada Song”) during a prison break and The Runaways’ “Cherry Bomb” during an action scene. The music humanizes the film much in the way Pratt’s sly, affable performance humanizes Peter — he’s a hero, sure, but he’s basically an overgrown boy, his messy spaceship like a big floating treehouse.

Peter gets the orb, and immediately becomes the target of Gamora (Zoe Saldana), the adopted daughter of bad-guy Thanos (Josh Brolin) who is apparently interning with another bad guy Ronan (Lee Pace). Ronan is a bad-guy in the typical kneel-before-me Marvel mode, who wants the power of the orb to destroy the rival Xandar race. While Gamora is trying to get the orb, Peter is being chased by two bounty hunters; Rocket is a tough-talking cyborg raccoon (voiced by Bradley Cooper), and Groot (voiced by Vin Diesel) is a sentient tree man who can only say three words, “I am Groot.” It works for him.

Eventually, they all get thrown in jail, where they also meet Drax (wrestler Dave Bautista), and the five of them decide to join forces to sell the orb and, eventually, stop Ronan.

Much of this sounds like every other Marvel movie (okay, except for the raccoon and the talking tree), but in this case it’s the singer, not the song. Gunn takes his characters more seriously than his action, and finds a lot of humor and not a little poignancy in this band of misfits who can’t possibly live up to the “Guardians of the Galaxy” moniker. They’re like the Goonies thrust into an epic space opera, and you root for them as they wrestle with their own feelings of inadequacy (yes, even a raccoon has issues) and rally to save the day.

I was probably hope for something a little more revelatory from “Guardians,” which does sink into the usual protracted, visual-effects heavy fireworks finale that Marvel can’t seem to get away from. Sure, it’s fun to watch spaceships collide into each other, and good guys battling bad guys and all that. But I could watch a “Guardians” movie that’s just the five of them sitting around a table with a pitcher of beer and a deck of cards. Hard to say that about the “X-Men.”