There’s an early gag in Trainwreck, the new comedy written by and starring Amy Schumer and directed by Judd Apatow, in which our protagonist, also named Amy, stumbles home with a new male conquest and watches him disrobe. When the fellow drops trou, she is both astonished and appalled at the extent of his manhood. “Your dick doesn’t end!” she exclaims.

I wasn’t sure when I saw the film (and I’m still not) whether this was a cunning bit of self-mockery: Apatow’s raunchy comedies have consistently been chided for their excessive length, and Trainwreck, which clocks in at just over two hours, is no exception. This is a movie from which 15 or 20 minutes could have been profitably trimmed.

Which is to say that my harshest critique of Trainwreck is that it offers too much of a good thing. This exquisitely rude rom-com is the most flat-out hilarious film to hit screens in many moons, a big-screen breakout for Schumer and a return to form for Apatow after the disappointment of This is 40. (I was, and remain, a committed defender of the oft-maligned Funny People.)

Following a prologue in which Amy’s father (Colin Quinn) explains to his young daughters the impossibility of monogamy by way of a child’s doll (“What if I told you this was the only doll you could ever play with for the rest of your life?”), we flash ahead 23 years to find the grownup Amy taking her dad’s advice to heart. Her encounter with the over-endowed paramour is merely one of a series of interchangeable one-nighters. Groggily waking up in one strange bed, she prays, “Please don’t be a dorm room, please don’t be a dorm room,” only to discover a reality almost as horrific: Staten Island. (Her shame-ride back to Manhattan, however, proves admirably shame-free, as she Titanic-poses on the guardrails of the Staten Island Ferry.) Amy does have one regular fella, the walking HGH-supplement Steven (a surprisingly funny turn by WWE star John Cena). But following her sublimely unsuccessful effort to coach him to talk dirty, it’s all downhill for that relationship.

This exquisitely rude rom-com is the most flat-out hilarious film to hit screens in many moons.

Amy works for a glossy magazine memorably titled S’Nuff, which under the leadership of its editor, Dianna (a gloriously wicked and glammed-up Tilda Swinton), specializes in articles such as “The S’Nuff Guide to Beating Off at Work” and “Ugliest Celebrity Kids Under Six.” But when Amy is sent out to write a feature on a charmingly nerdy, borderline-virginal sports doctor, Aaron (Bill Hader), she discovers to her great surprise that she rather likes him.

The narrative that unfolds from this premise is not a novel one, but Schumer’s caustic wit keeps the story on its toes. Even as we watch Amy and Aaron begin to fall for each other gauzily, Amy punctures the moment in voiceover, declaring, “I hope this love montage ends like Jonestown.” Several scenes (the magazine story pitch meeting, the bridal shower) are reminiscent of Schumer’s TV series, and the overall tone, while less political, is no less biting. There are sharp comic drive-bys of Willy Wonka, Keyser Söze, Kanye West, and Lifetime movies, as well as what is almost certainly the best Alex Rodriguez joke of all time.

Schumer herself is a magnificent mess as Amy, and Hader’s quirky likability has never been put to better use. And even beyond Swinton and Cena, the supporting cast is uniformly terrific: Quinn as Amy’s belligerent dad; Brie Larson as her settled-down younger sister; Vanessa Bayer as her co-worker and best friend; Dave Attell as the acerbic homeless guy who claims a chunk of sidewalk outside her apartment.

But perhaps the movie’s greatest surprise is the comic chops displayed by NBA god LeBron James, who plays a version of himself as Aaron’s patient and off-work buddy. (This may be the cleverest counter-self-portrait since Michael Cera’s coke-addled sex fiend in This is the End.) Schumer and Apatow deftly avoid saddling James with more than he can handle, and he nails the material he’s given—most of it revolving around his super-sized love for the city of Cleveland, his exceptional frugality, and his profound concern for Aaron’s romantic prospects.

The movie drags a touch in its final third (an “intervention” scene plays as exactly what it is: an unnecessary excuse for additional celebrity cameos) before coasting into a decidedly Apatowian happy ending. The director has always deployed dirty jokes in the service of conventional values—monogamy, parenthood, marital perseverance—and a number of critics have already faulted the film for its lack of cultural daring in this respect. (I confess that I’m not entirely convinced this is a bad thing.) Is Trainwreck essentially a gender-inverted variation on Knocked Up? Sure it is. But that in itself represents progress.

In any case, this is a film that belongs not to its director but to its star, who, if there is any justice in the world, is about to ascend from cult icon to mass phenomenon. Schumer will almost certainly have many opportunities to deploy her edgy wit toward edgier ends. I can hardly wait.