Has Juno backlash lasted this long? Early returns on the Rotten Tomatoes chat boards suggest so, as hysterical fanboys take turns skewering screenwriter Diablo Cody’s Oscar-winning debut and predicting dire things indeed for her latest, the hugely entertaining horror-comedy Jennifer’s Body.

Bashing Juno? That’s so 2007. It’s true that Cody’s dialogue is sometimes gratingly self-satisfied, laced with glib pop-culture references and slang that sounds more scripted than organic. That hasn’t changed. But there is something approaching brilliance in Jennifer’s Body, her macabre tale of teenage friendship gone awry in the sleepy backwoods of Devil’s Creek, Minnesota.

I’ve heard Jennifer described as a cross between Evil Dead II and a John Hughes movie. That’s about right. If you want blood, you’ll get it. But Cody and director Karyn Kusama (Girlfight) seem less interested in cheap scares than in something more substantive: exploring the purgatorial existence of teens caught between being kids and adults.

“Hell is a teenage girl,” we’re told, and witnessing the feud that estranges Jennifer (Megan Fox), a high-school alpha female, and Needy (Amanda Seyfried, of Mamma Mia!), the BFF who has lived in her shadow, it’s easy to believe. The story begins, not so innocently, at the local rock club, where a band from the big city is secretly prowling for a virgin to sacrifice. Their deal with the devil seems to be sealed when Jennifer, unsuspecting, volunteers to ride in their van.

Jennifer is no virgin, making her sacrifice somewhat problematic: Rather than surrendering her body to Satan, she returns as a flesh-hungry monster. Needy is horrified, yet hope for a reconciliation endures, even as the body count rises. Needy is everything Jennifer isn’t, and wasn’t – approachable, loyal and timid when it comes to boys. Even with her adorably nerdy boyfriend Chip (Johnny Simmons), Needy is bashful.

Instead of dismissing the reborn Jennifer outright, Needy seems to sympathize, particularly during one provocative scene in which they kiss, at length. But when Jennifer sets her sights on Chip, all bets are off.

The violence in Jennifer’s Body is so over-the-top that it can’t be taken seriously, and I think that’s the point. This is a comedy at heart, and a sharp one. Even when self-indulgent – but more often when it’s not – Cody’s dialogue can be insightful, and Kusama frames her story stylishly, paying homage to genre classics like Carrie and A Nightmare on Elm Street. The movie knows its history and playfully tweaks it, but without seeming derivative or ironically detached.

Fox, whose acting has been overshadowed in Michael Bay’s Transformers movies by towering explosions and CGI bots, is a natural femme fatale who is perfectly cast as the high-school heartbreaker; she has a dismissive sneer that could bring boys of any age to their knees. Yet it’s Seyfried, convincingly pulling off the transition from mild-mannered innocent to Buffy-style demon slayer, who serves as Jennifer’s rapidly beating heart. (Also excellent are J. K. Simmons, as a clueless teacher, and Adam Brody, as the soulless, Satan-worshipping worm who – what else? – fronts an emo band.)

There is tragedy in Jennifer’s downfall, and in the bitter dissolution of her friendship with Needy. But there is uplift as well. Even in hell, the ending seems to suggest, the bad guys don’t always win.