The MPAA reserves its NC-17 rating for only the seediest, most sexually explicit of films. The umbrella of the R rating is a broad one that covers even the raunchiest of material, and it typically takes catastrophic sexuality to warrant the more extreme mark.

It’s quite a feat, really, to receive an NC-17 rating. The tag typically spells disaster at the box office and is avoided almost universally by the best auteurs.

But sometimes fleeting shots of lukewarm sensuality and quasi-muffled cries of coital meridian are not enough to slake a director’s lust for primal filmic eroticism. Some itches are just too big for the R rating to scratch.

“Lust, Caution” is one of these films.

Set in Japanese-occupied Shanghai in the midst of World War II, “Lust, Caution” is centered on Wang Jiazhi (Wei Tang), a university student turned resistance fighter who is recruited to espy and seduce the traitorous government official Mr. Yee (Tony Leung). When Wang’s mission of espionage turns into an elicit affair, her loyalty is tested and the success of the resistance hangs in the balance.

The movie’s most immediate allure is its atmosphere. Superb costumes and art direction coupled with ravishing cinematography from Rodrigo Prieto transport the viewer straight into the heart of 1940s China. Automobiles hum along shop-lined streets of expertly dressed elites. Rickshaws creak down dim alleyways patrolled by scowling Japanese guards.

Aesthetically believable and remarkably photographed, “Lust, Caution” is an attractive picture top to bottom.

The highlight of the film is undoubtedly the performance of newcomer Wei Tang. In her first feature, she delivers a savage performance as the film’s enigmatic heroine. Going toe-to-toe with Asian cinema giant Leung (“In the Mood for Love,” “Hero”), she matches, even bests his merciless performance.

Vulnerable one moment and salacious the next, her virginal deportment effortlessly denatures into agonizing carnality. Tang delivers an unabashed performance that is certainly one of the year’s best.

No matter which way you shake it, “Lust, Caution” is about sex. Beginning to end, lust and depravity saturate the film. Sex is its draw and, sadly, also its downfall.

The sex scenes are some of the most brutal moments I have ever seen on film.

Nothing is censored. Full-frontal male nudity, orgiastic shrieks of crisis and tight shots of the coitus itself comprise these scenes. Few times before has sexual congress on film been more virile, more unspeakable.

Tang and Leung do a masterful job of making their raw intimacy authentic. Leung winces his brow, gnarls his teeth and nearly bites in the throws of intercourse.

Tang is so convincing she’s almost hard to watch. Her moans and spasms emote at once excruciating pain and unbridled ecstasy. She sells it so well that one cannot help but think she is herself aroused.

“Lust, Caution” is a libertine ode to sex in cinema. But for all its sensuality, it fails to engender real intimacy or meaning.

The film’s unabashed sexuality does as much to disgust as it does to arouse. It’s not poetic; it’s barbaric. Devoid of emotion or any shred of poignancy, the sex scenes are reduced to well-lensed pornography. I found myself sinking slowly into my seat, wanting to crawl out of the theater and atone for my indiscretion.

The barbarism is not moving, only frustrating. With each frame the viewer becomes increasingly alienated from the story and more detached from the characters – it’s nearly impossible to feel a thing for any of them. There is nothing to love and little to hate.

Taiwanese director Ang Lee is one of today’s finest and most celebrated filmmakers. His films “Crouching Tiger, Hidden Dragon” and “Brokeback Mountain” are two of the best, most influential films of this decade. Along with Korean brethren Wong Kar-wai and Chan-wook Park, Lee is at the apex of Asian filmmaking, bringing the best of Far East cinema to American viewers and beyond.

As difficult as it is to say, and as nearly impossible as it is to believe, “Lust, Caution” is one of Lee’s “least Asian” films. Eastern filmmakers (like Kar-wai) are renowned for long shots, whispered dialogue and reflective mood. “Lust, Caution” is remarkably Western: choppy, disjointed and obvious.

Lee abandons the unique contemplativeness typical of Eastern cinema. Pacing is entirely off. At times, the film drags. Elsewhere, it feels rushed. The first 40 minutes of the film are agonizing and could be reduced to 15 – too much foreplay. Just when the story begins to swell with intrigue, it loses stamina and falls limply into a disappointing finish.

Lee’s direction is solid, as always (earning him the Golden Lion at the Venice Film Festival), but it lacks necessary restraint. Although daring, even admirably so, the film’s blatant sexuality is more unsettling than it is powerful and left yours truly feeling dirty and violated.

Less lust and more caution would have gone a long way in making Lee’s film more attractive.

Despite its vicious sexuality and white-hot leading performances, “Lust, Caution” fails to ever reach climax – an audacious effort with a half-cocked result that leaves audiences spent and unsatisfied.

“Lust, Caution” is currently playing at the Bryn Mawr Film Institute.