The modern American romantic comedy has reached such a saturation point that the formula is no longer enough--there are no real stakes and no real suspense, because the construction is assumed and the resolution is a foregone conclusion. Boy will meet girl, they will fall for each other, complications will ensue, outside factors will conspire to keep them apart, but all will eventually right itself in the end, and they shall live happily ever after, tra la la. Every once in a while, an inventive filmmaker will shake up the formula, but more often than not, it becomes a matter of what kind of shading they do when they color in between the regular lines. Whatever interest is generated is found in the specifics, the details, the things happening in the periphery: supporting performances, subplots, slightly skewed perspectives. In last summer's Going the Distance, for example, the memorable moments were not provided by the leading actors and their predictable predicament, but by the film's unexpectedly dirty mouth, by the funny cameos from comics like Mike Birbiglia and Kristen Schaal, by the glorious weirdness of Charlie Day. Ivan Reitman's new sex comedy No Strings Attached is a painfully calculable narrative; anyone who doesn't know exactly how it will go should get out more. But there is a good line here, an enjoyable supporting actor there, and in the middle of it, there is Natalie Portman in a performance of genuine comic ingenuity and inventiveness.

The story begins 15 years ago (to the strains of Color Me Badd's "I Wanna Sex You Up," which came out 20 years ago, but never mind), when Adam and Emma meet at summer camp and don't quite hit it off. Flash to ten years later, where the pair (now in the personages of Portman and Ashton Kutcher) meet again at a frat party; he's clearly taken with her, but she warns him off. She's unemotional and not one for relationships and all that stuff. Fast forward again, to a year ago (there's a lot of set-up), as they connect again, and become friends; he turns to her when he finds out that his famous father (Kevin Kline) has started dating one of Adam's exes. She's still not one for attachments, so she proposes a "friends with benefits" situation; he gladly goes along because, you know, she looks like Natalie Portman.

Plus he likes her. One of the refreshing elements of Elizabeth Meriwether's screenplay (and there isn't an abundance of them) is in its reversal of traditional sex roles--Adam is the romantic, Emma's just in it for the booty. Also welcome is the film's casual (and authentic) attitudes about modern female sexuality; the four-letter words and cavalier disposition are (again) reminiscent of Going the Distance, but without that film's somewhat obvious self-consciousness.

The supporting cast is stuffed to the gills with terrific actors, few of them fully utilized but all valuable: Greenberg's Greta Gerwig and Mindy Kaling (from The Office and the Twitter) as Portman's roommates, Chris "Ludacris" Bridges and the invaluable Jake Johnson as Kutcher's buddies (Johnson gets about half of the film's good lines), Olivia Thirlby perfectly cast as Portman's sister, Abby Elliot from Saturday Night Live as a potential hook-up. Cary Elwes, though, gets an absolute nothing of a role, and while Kevin Kline is always welcome, his early scenes with Kutcher are surprisingly unfunny--and off-rhythm, as seasoned comedy director Reitman keeps holding for laughs that just aren't there. (That's not the only time his pace fails him--more on that presently.)

But the picture's MVP is Portman--she looks great, she's consistently likable, her comic timing is exquisite, and she makes even a weak line (like the drunken explanation that she's "just studying for the doctor test!") sing. As someone who still has trouble shaking the image of the 12-year-old from Leon, this viewer was also fully convinced by her matter-of-fact sensuality, particularly in a scene of post-coital analysis ("That was a really good call," she tells Kutcher, of one successful move). She's so good, in fact, that she makes the reliably irritating Kutcher better, just by sharing the screen with him.

However, for all of the pleasures of her performance, the film doesn't work. Too much time is spent trying to convince us that the horrifying High School Musical-style teen show where Adam works (and hopes to write) is any good; after their first synth-pop number, we keep waiting for the punch line. There isn't one, aside from Reitman cameoing as the show's director, saying how great it was. Surely there is humor to be mined from pre-fab tween television, but none is even attempted here. We're supposed to believe that it's an awesome show, and hope hope HOPE that sweet Adam gets a job writing this pap. The eventual romantic complications are, as noted, completely expected, and are delivered as unimaginatively as they were conceived.

And then there's the third act. The endless, monotonous, interminable third act, which smashes in complications and resolutions and crises like a particularly ugly highway pile-up--there is an angry parting of ways, and montages of life going on, and a wedding, and a big party, and a mistaken sighting with a new partner, and God help us, even a visit to the emergency room. At 110 minutes, No Strings Attached is a good 30 minutes too long; as that perpetual climax keeps spinning and spinning, we can barely comprehend how a comic director once as skilled and savvy as Ivan Reitman (c'mon, the guy did Stripes and Ghostbusters) can so thoroughly lose his sense of pace.

As No Strings Attached stumbles and careens toward the single most foreseeable closing shot in recent rom-com history, most of our goodwill towards it has long evaporated--for everything that's stuffed into its final third, most of the interesting things around the picture's edges have fallen away. It is ultimately just another--yet another--story about a boy and a girl who overcome a bunch of irrelevant bullshit so they can provide the audience with the happy ending they came for. If you're part of that audience, well, go to it. In the meantime, here's hoping Portman eventually finds a comic vehicle that's worth her time.

Jason lives in New York. He holds an MA in Cultural Reporting and Criticism from NYU.