Gal Gadot in “Wonder Woman 1984.” Clay Enos/Warner Bros. Pictures/DC Comics.

It’s not often that a movie is a genuine game-changer. In 2017, “Wonder Woman” became just that, as a superhero movie featuring a female protagonist that went on to become a huge hit – proving that little boys are just as interested in seeing a woman save the day as little girls.

At least for a while, “Wonder Woman 1984” carries that groundbreaking realization with a lightness that was the first movie’s secret all along. As the title suggests, “WW84” takes place in the 1980s, when the dress-for-success rules included commuter tennis shoes and linebacker-worthy shoulder pads. Throughout much of the film, women get hit on, harassed and assaulted with grim regularity, presumably to remind the #MeToo-era audience that, as Gloria Steinem famously observed, sexist depredations women routinely suffered were once just called “life.”

That recurring motif is the closest thing to feminist polemic in a movie that’s more interested in getting on with it – with humor, bravado and panache – than proving a point. “WW84” opens with a glorious set piece on the Amazonian island Themyscira, where a young Diana (Lilly Aspell) is participating in a contest of endurance, skill and physical derring-do. As she makes her way through the daunting obstacle course, it’s clear that the only way out is through – by way of somersaults, pirouettes, impressive trick-riding and giant leaps for womankind.

Little Diana learns a life lesson that day at the hands of her elders (Connie Neilsen and Robin Wright), having to do with patience, diligence and honesty. At that point, “WW84” cuts to “present” day, when grown-up Diana (Gal Gadot) is working at the Smithsonian and Washington, D.C., is awash in such ’80s-tastic signifiers as inline skates, leg-warmers, popped collars, packed shopping malls and Reagan-era greed, personified by a TV scam artist named Maxwell Lord (Pedro Pascal).

So far, so playfully retro. And things get even more goofy when Diana meets a nerdy colleague named Barbara Minerva, played with self-deprecating earnestness by Kristen Wiig. Her museum has just received a cache of stolen valuables, including a gemlike stone sitting atop an inscribed plinth. It’s made clear early on that the rock possesses supernatural powers, magical properties that will bring Diana, Barbara and Maxwell Lord into an epic fight between – what else? – good and evil.

The same elements that made “Wonder Woman” such a pleasure to watch are present in “WW84,” including the supremely self-possessed Gadot, who plays the title character with the same grace and understatement she brought to the initial installment. And, as in the first film, she’s at her best when she’s playing off a vivid supporting character: Here, that honor belongs to Wiig, whose kooky persona is the perfect foil for Gadot’s watchful reserve. Even more gratifyingly, filmmaker Patty Jenkins has found a way for Diana’s love interest, Steve Trevor, to time-travel back into her life, meaning that Chris Pine has time-traveled back into ours. Gamely throwing himself back into the love-interest role commonly reserved for ingénues, he steals every scene he’s in, whether in a Mystery Date-like fashion montage (all hail the fanny pack) or being introduced to such modern-day phenomena as D.C. Metro escalators and the great works of the Hirshhorn.

For the first hour and a half, “WW84” is a delightful flight of escapist fancy, with Diana and Steve’s love story ensconcing itself comfortably, if a bit talky, within the confines of an action adventure. Then, at the 90-minute mark, it’s as if Jenkins remembers her other deliverables, in the form of special effects, epic global crises and a plotty, ever-more-muddled story line that metastasizes into something much darker and more violent.

Once “WW84” makes that pivot, it slides into superhero boilerplate, with the intelligence and high spirit that distinguishes the franchise drowned out in dull CGI stuff-for-stuff’s-sake. The shift underscores the contradictions that have bubbled under the surface of comic book movies since they began taking over Hollywood 20 years ago: As movies that both kids and their parents can enjoy together, they’ve become the closest thing we have to wholesome, old-fashioned family pictures. But they also aspire to artistic sophistication, necessitating “deep” themes and serious-minded mayhem. Toss in a limited and self-referential vocabulary of chases, explosions, standoffs and last-ditch rescues, and you get a cinematic language stuck in a tiresome case of diminishing returns.

For “WW84,” that means that viewers are treated to two movies: The first one, that hits its marks with the sure-footedness of young Diana making her way through Themyscira’s backcountry, and a second one that feels bloated, grandiose and drearily overblown. The “Wonder Woman” movies have the benefit of a fabulous central character and just the right actress to play her. With luck, future iterations will focus on the franchise’s greatest strengths, which were never hyperbolic or even super-heroic, but quirkily, endearingly human.

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