When life gives you giant radioactive cockroaches, you say, "Okey dokey!"

At least you do if you're Lucy (Ella Purnell), the eternally optimistic protagonist of Amazon Prime's "Fallout" (streaming Wednesday, 9 EDT/6 PDT, ★★★ out of four). The crux of the adaptation of the popular post-apocalyptic video game series is the contrast of Lucy's peppy step with the backdrop of a desolate, violent and dirty world, 200 years after nuclear armageddon. Silly against serious. Americana against anarchy. A future stuck in the past.

This retro-futuristic style comes to life in vivid Technicolor in the series, which feels like the video game come to life in the best way possible, full of exaggerated costumes, cartoonish violence and very big guns. But there's a strong story underneath all those 1950s outfits and two-headed cows. "Fallout" is very aware that its roots are fun, but not mindless. And while there is plenty of room in the zeitgeist for sober and emotional game adaptations (HBO's "The Last of Us") and also for the juvenile ("The Super Mario Bros. Movie"), "Fallout" finds a unique and lively place in the middle.

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"Fallout" starts with Lucy, a plucky young citizen of Vault 33, a clean and safe fallout bunker occupied by the decedents of those rich enough to afford a spot back in the 1950s when the U.S. and the Soviet Union nuked each other into oblivion. The world of the vault is full of '50s kitsch and can-do spirit; Lucy believes she was born to "save America." But when raiders from the lawless surface break into the bunker and kidnap Lucy's father (Kyle MacLachlan), she decides to brave the nuclear wasteland to save him.

There's also Maximus (Aaron Moten), a lowly grub in the psuedo-religious "Brotherhood of Steel" military who wants to be a "knight" and drive a mechanized power suit (think of a more buff Iron Man). And most enigmatic of all is the Ghoul (the always delightful Walton Goggins), a mutated, deformed being who's lately buried alive. The three eventually connect as Maximus and the Ghoul pursue a mysterious doctor (Michael Emerson) whom Lucy happens to run into. The Ghoul wants a bounty, Maximus wants to impress his superiors and Lucy might be able to get her dad back with the doctor's help. That's if they aren't killed by irradiated bears along the way.

Unfortunately, Maximus' character arc and storyline is by far the weakest aspect of the series. Neither the scripts nor Moten give the character depth or understandable motivation. Even the intentionally ill-defined Ghoul comes off as a more self-assured character. And worse, it's in the complex, jargon-y "Brotherhood of Steel" that the sci-fi gobbledygook starts to sound like white noise, even if you love hard sci-fi.

Still, two out of three strong leads ain't bad, and Purnell ― with her anime eyes ― and Goggins with his mischievous grin are more than enough to carry "Fallout" across the wasteland. Series creators Geneva Robertson-Dworet ("Captain Marvel") and Graham Wagner ("Silicon Valley") are loyal to the game's spirit, yet wisely avoid common video game adaptation clichés, like an overreliance on "first-person" perspective and a too-literal recreation of the original story. Opting for an new narrative that simply takes place in the "Fallout" world, the series is a mix of adventure and puzzle-box mystery, with more than enough action scenes to satisfy the RPG faithful. It's fun, and only occasionally overcomplicated.

And if the violence is quite frequent and exquisitely graphic? Hey, it all gels in a fictional world where Goggins doesn't have a nose.