With 2005's "The Squid and the Whale" and 2007's "Margot at the Wedding," writer-director Noah Baumbach demonstrated a distinct fascination with the dark and oft-times ugly side of human behavior. This trend continues with "Greenberg," and it has started to grow tiresome, becoming a detriment to not only one's enjoyment of his films, but to characters whose difficult, self-destructive personalities halt them from ever moving forward. Movies about insufferable people don't have to be insufferable themselves, but when a tangible arc is lacking and no credible change is made in who they are from beginning to end, the viewer is left to question what, exactly, the point is.

When well-off entrepreneur Phillip Greenberg (Chris Messina) leaves Los Angeles with his family for a three-week trip to Vietnam, his troubled older brother Roger (Ben Stiller) moves in while they are gone. It is here that Roger—on the verge of turning 41 as he wonders where the time has gone—runs into Phillip's dedicated 25-year-old assistant Florence (Greta Gerwig). An aspiring singer still trying to find more than her voice, Florence is at first stand-offish with Roger (she's been told he was recently released from a mental hospital) and then, against her better judgment, drawn to him. The courtship between these two quirk-filled individuals, however, is anything but carefree and easy.

A comedy-drama so subdued as to have little effect as either, "Greenberg" goes on its muted, unhurried way without a care to its plot or a typical three-act structure. For a while, watching the characters go about their everyday lives is enough—Florence deserves her own movie, preferably a better one—but at some point there has to be a major development or event of importance to give the film's existence purpose. That moment ultimately never comes. The characters do not noticeably grow or evolve. Their lives, from start to finish, are not changed. And as for the relationship between Roger and Florence, it is one built on a wobbly foundation that could collapse at any second beyond the last frame. Both characters, one regrettably suspects, are doomed to disappointment.

In a, lately, too-rare serious performance, Ben Stiller (2008's "Tropic Thunder") is plausible as Roger Greenberg, but the character is too erratic to be a plucky hero or even a mildly likable protagonist. It is never explained why Roger went to the loony bin, but he does exhibit signs of depression over his career failures (he once was in a rock band that dismantled before it hit big) and Obsessive-Compulsive Disorder (he writes to corporations daily with piddling grievances). Furthermore, he's just plain unpleasant to be around, nice one minute and verbally berating Florence and his best friend/former band-mate Ivan Schrank (Rhys Ifans) for no apparent reason the next. His cruel treatment of Florence is the deal-breaker in getting behind these two as a couple. Even if she doesn't think so now, she deserves far better than what he offers her. Devising a slim contrivance—Phillip's sick dog, whom Roger and Florence both care for—as a means for both parties to continue seeing each other after they've ended things comes off as strained.

Writer-director Noah Baumbach hasn't much for Florence to do after he has sharply established her in the opening ten minutes, but that lack of maturation doesn't hinder the lovely work Greta Gerwig (2009's "The House of the Devil") does. A scene-stealer in the past who has just hit what should serve as her big-time breakthrough, Gerwig is so fresh, so natural, so effortless, so sympathetic, and so unlike most of her like-aged Hollywood starlet counterparts that what she does with her performance is nothing if not original. Florence is a fascinating character, to boot—one who is always aware that time is passing her by, yet hasn't figure out what to do with it yet—but what attracts her to Roger is left unexplained. Leaving his company humiliated and teary-eyed nine times out of ten, Florence does her best to avoid him thereafter, but keeps getting drawn back into his web. In turn, Roger's apologies are half-hearted. He expresses a desire to change, sure, but he never actually does. If Florence thinks they may have a future together by the end, she's fooling herself. He's first and foremost a sick, unhappy man who probably shouldn't have left that mental hospital after all.

Suffice it to say, "Greenberg" is an anemic motion picture, well-intentioned and not without its small-time pleasures, but thoroughly bereft of a satisfying destination for its already slim plot. With the supporting players only getting a couple scenes apiece and none of them making the biggest of impressions, the focus remains on the problem-ridden travails of mismatched couple Roger and Florence. The Los Angeles milieu is brought to accurate, unfussy life through cinematographer Harris Savides' (2009's "Whatever Works") lensing and Baumbach's lovingly chosen soundtrack (memorable song cues include The Steve Miller Band's "Jet Airliner," Albert Hammond's "It Never Rains in Southern California," and Paul McCartney's "Uncle Albert/Admiral Halsey"), but these positives are but fleeting detours in a film that disappointingly goes nowhere, and does it slowly.