As advertised, there's a whole lotta sex in John Cameron Mitchell's Shortbus. Men with men, women with women, women with men and all possible multiplications and permutations thereof. Which really shouldn't be surprising, since the film is quite aggressively about sex. Unlike the great majority of cinematic sex scenes -- most of which are blocked and scored so carefully that they're more like choreographed, showy dances than anything else -- those in Shortbus are no mere window dressing, and nor are they present as excuses to get pretty people to take their clothes off (and then be artfully covered by that old Hollywood favorite, the L-shaped sheet). Instead, they're crucial to the plot, and to the development of the characters in the film. And they're also a whole lot of fun, much of the time. Mitchell and his cast very successfully avoid both the falseness of mainstream sex scenes and the bow-chick-a-bow-bow absurdity of straight-up porn, arriving instead in a place of realism, where actual people have actual sex. Sweaty, awkward, joyous, sad sex that's not always either pretty or sexy.

Based on a story created by Mitchell and his cast in workshops before filming began, the film focuses on a small group of post-9/11 New Yorkers. Like all of us, they're fully-formed individuals with imperfect lives: We meet Sofia (Sook-Yin Lee) a sex therapist who has never had an orgasm (she calls herself "pre-orgasmic"); James and Jamie (Paul Dawson and PJ DeBoy) "the perfect couple" who, after five years together, are considering opening their relationship up; and Severin (Lindsay Beamish) a miserable dominatrix who has lots of orgasms but is almost incapable of intimate, human interaction. Over the course of Shortbus, all four acknowledge the deep, profound holes in their lives and, rather than continuing to paper them over like so many of us do, with the help of those around them they struggle through the agony of unblinking personal examination, hoping to come out intact on the other side.

Despite its undeniably melancholy undertones -- the movie darkens as it goes along, and the ostensibly joyous final scene is haunted by a terrible feeling of loss -- there's great warmth and humor to Shortbus. Several scenes (including that patriotic threesome you've heard so much about) are laugh-out-loud funny, and the mostly amateur cast acquits itself well. Lee, a Canadian music/media personality (who, by the way, went back to her day job with CBC Radio yesterday -- it's hard to imagine a public face of any American media organization not being fired after engaging in unsimulated on-screen sex and masturbation), is particularly impressive as Sophia. Smart enough to know she's a mess, Sophia is used to quickly solving problems; when she can't fix herself, her frustration is explosive, and Lee gleefully inhabits the character in all her jagged, aggressive, vulnerable glory.

As impressive as it sometimes is, Shortbus is not without its flaws. Alongside all the wit and fire, there are also moments of dreadful triteness (Oh look, a smart, deep, suicidal depressive!) and unintentional absurdity (Sex with your stalker? Brilliant!) in the movie, and they can't help but mar its overall effect. Despite those failings, however, Mitchell's film remains both admirable and moving. It's easy, after all, to make a movie about sex -- throw some naked bodies in front of the camera, and you're pretty much there. But it's something else entirely to make a movie about sex that has warmth and depth, and offers more than just physical arousal; Mitchell should be applauded for achieving the nearly impossible task of making a sex-laden film that stimulates our minds above all else.