"Guardians of the Galaxy Vol. 2," much like its 2014 sleeper-blockbuster predecessor, cruises to victory on a wave of irresistible '70s pop-rock earworms. There are plenty of other attributes, too—a game cast bursting with chemistry; a tone at once tongue-in-cheek and unabashedly sincere; a writer-director in James Gunn who favors characters and heart over soulless interstellar battles and pyrotechnics—but whenever things threaten to verge on the old-hat, a groovy soundtrack chestnut will swoop in to complement the onscreen goings-on. Of all the films within the Marvel Cinematic Universe, this series' cheerful embrace of its own freak-flag quirkiness gives it the edge over more well-known comic-book properties. If the pressure to live up to the rightfully acclaimed first picture is sometimes apparent in its foundation, "Guardians of the Galaxy Vol. 2" nonetheless does exactly what a successful sequel should, building upon and bringing added complexity to the world which has been built and the people whom reside in it.

Abducted from Earth twenty-six years earlier following the cancer death of his mother (Laura Haddock), Peter Quill (Chris Pratt) has made something of a name for himself as an intergalactic good-guy mercenary. Soaring through space alongside his new makeshift family and team—green-skinned former assassin Gamora (Zoe Saldana); burly widower Drax (Dave Bautista); genetically engineered raccoon Rocket (voice of Bradley Cooper), and tiny humanoid tree creature Baby Groot (voice of Vin Diesel)—he has never been able to escape the feeling that a piece of who he is is missing. Hunted by High Priestess Ayesha (Elizabeth Debicki) and her Sovereign planet's gold-skinned, bioengineered-to-perfection minions when an offhanded remark (and a little thievery) from Rocket gets the group in hot water, the Guardians are narrowly saved from annihilation by Peter's long-lost birth father, the "god-with-a-lowercase-g" Ego (Kurt Russell), and Ego's kind-hearted, socially awkward servant Mantis (Pom Klementieff). Peter cannot quite believe his luck in finding his missing parent, and even more surprised to discover he has inherited some of his dad's unique celestial abilities.

"Guardians of the Galaxy Vol. 2" is joyous, silly, heartfelt, and occasionally majestic, a space opera with a distinct rhythm and a beloved Walkman in its arsenal. It's sci-fi, action, comedy and drama all rolled into one, situated in fantastical far-flung places yet with enough time left over for characters to discuss, for example, the intricate parallels they see between themselves and the lovelorn sailor sung about in Looking Glass' "Brandy (You're a Fine Girl)." The plot's trajectory, which has been blessedly kept out of the film's advertising, includes genuine surprises and a particular interest in the characters' lives—where they come from, what has led them to their current situation, and the steps they will take to move on as best they know how.

It helps to have such distinct actors and personalities on hand to build the Guardians' occasionally bickering and exasperated but certainly loving familial unit. Chris Pratt (2016's "Passengers") and Zoe Saldana (2016's "Star Trek Beyond") continue to beautifully essay Peter Quill (a.k.a. Star-Lord) and Gamora. The "unspoken thing" between them, which Peter likens to Sam and Diane on "Cheers"—an Earthbound reference Gamora clearly does not get—leads to a "will-they-or-won't-they?" tension and one lovely moment where the smooth sounds of Sam Cooke's "Bring It On Home to Me" prove too much for them to resist a slow dance together.

Dave Bautista (2015's "Spectre"), as Drax, comes into his own here, quick with shrewd comic line deliveries and an underlying warm affection for his friends. His burgeoning bond with the earnest, quirky Mantis, not yet confident in interpersonal interactions, is winning, and Pom Klementieff (2013's "Old Boy") is a lovable standout. Rocket, meanwhile, is fierce, unfiltered, yet somehow still cuddly, indelibly voiced by Bradley Cooper (2016's "War Dogs"), while Baby Groot is, well, every bit as adorable as one could hope. New to the series as Peter's father Ego, Kurt Russell (2017's "The Fate of the Furious") is exceptional in a role more layered than initially meets the eye, and an opening scene set in 1980 uncannily transports Russell back in time via flawless effects wizardry to the way he looked during the era of 1981's "Escape from New York."

In a movie that could have been overstuffed but never feels like it is, Gunn also makes room to further explore Yondu (Michael Rooker), the hard yet protective ravager who snatched a grieving Peter from his home planet and raised him all those years ago, and the antagonistic Nebula (Karen Gillan), torn between wanting adopted sister Gamora dead and hashing out her pent-up resentments. Karen Gillan (2014's "Oculus") takes advantage of the extra meat given to her complicated villainess; by the end, she is more than simply a lethal loose cannon, her proclivities bred from a specific understandable place.

As effortless as the first "Guardians of the Galaxy" felt, "Guardians of the Galaxy Vol. 2" appears to be trying a little harder to match what came before. Writer-director James Gunn ultimately prevails in spite of a handful of scenes where emotions strike as more manipulative and forced. This is not to say it isn't affecting, or hugely entertaining; the film unapologetically and refreshingly wears its big, beating heart on its sleeve. What's most memorable, though, is that great soundtrack, and how each tune meaningfully relates to Peter's late coming-of-age. The song cues are impeccably chosen, and perfectly used; they are as much a character as any of the actors and seamless CG creations onscreen, just as the mixtapes Peter's music-loving late mother gave to him have been his dearest companion since he was spirited from his home planet as a child. From the witty opening credits sequence scored to Electric Light Orchestra's "Mr. Blue Sky," to the anthemic integration of Fleetwood Mac's "The Chain," to the dramatically resonant use of Cat Stevens' "Father and Son," to the significant threading of the aforementioned "Brandy (You're a Fine Girl)" throughout the narrative, the classic music injects energy, nostalgia and human connectivity into a genre that can too often strike as impersonal and mechanized. "Guardians of the Galaxy Vol. 2" is alive and thriving, a smart, thrilling, sweet-natured kickoff to the 2017 summer movie season.