Alexander Payne has to be the most unassuming great filmmaker in America. And the better he gets, the less attention he calls to himself: there's not a frame in his wonderful new movie "Sideways" that asks you to marvel at the director's virtuosity. Even more than "About Schmidt," which was dominated by Jack Nicholson, a huge presence even inside the skin of a mild insurance salesman, "Sideways" stays resolutely life-size. And that, in this age of hype and hyperventilation, may be the most radical thing about it.

This deceptively modest comedy leaves a long aftertaste. It follows two clueless middle-aged men making a last-hurrah tour of the Santa Barbara wine country before one of them gets married. Miles (Paul Giamatti) is a failed novelist who teaches eighth-grade English. A tightly wound bundle of anxiety and self-loathing, he's still licking his wounds from a bitter divorce. But all his self-pity and uncertainties vanish in the face of his passion for wine. As an obsessive, discriminating oenophile, he achieves mastery. He can wax rhapsodic about the personality of a pinot noir. The mere mention of merlot fills him with contempt.

The groom-to-be, Jack (Thomas Haden Church), his former roommate at San Diego State, couldn't be more different. A onetime soap actor now doing commercial voice-overs, he's an affable, vain southern California extrovert, a fortysomething party guy who still calls people "dude," insists on positive thinking and is as unaware of a good Sauvignon blanc as he is of his own unquenchable narcissism.

Miles envisions a relaxing week of wine tasting and golf. But Jack has other priorities for his last week of freedom--he wants to get laid. And he wants to shake Miles out of his two-year depression. "Don't go to the dark side, man," he warns his moody friend. Giamatti and Church are an inspired comic team, a Mutt and Jeff drawn with subtle novelistic detail. (Payne and his writing partner Jim Taylor based their screenplay on a previously un-published novel by Rex Pickett.) "Sideways" is a road movie about a classic odd couple, but nothing about it feels formulaic. Filled with ambivalent emotions and middle-aged panic, it's a comedy that gets funnier, and sadder, as it goes.

The movie hits its stride with the arrival of Maya (Virginia Madsen), a striking, down-to-earth waitress whose knowledge of wine rivals Miles's, and her friend Stephanie (Sandra Oh), a savvy, seductive wine pourer whom Jack puts the moves on. Their wine-fueled double date, which ends at Stephanie's house, is a marvel of ensemble acting and pitch-perfect writing. While Jack and Stephanie make a beeline to bed, Miles and Maya retreat to the porch, where they court by talking only of wine. When he tells her why he loves pinot noir, he's describing his own temperamental self; when she explains what the ever-evolving nature of wine means to her, she's revealing her soul. It's a beauty of a scene.

These romances are all built on lies--chief among them Jack's failure to mention he's about to get married. Soon enough the cats come tearing out of the bag, with hilarious, heartbreaking repercussions. Oh (who is married to the director) is a pure delight as the sensual Stephanie, who rocks Jack's easily upended world. Madsen, who's been wasted playing B-movie femmes fatales, blossoms as this smart, centered divorcee: Payne lets us see her--and "Wings" TV actor Church--in a whole new way. These are career-changing performances.

"Sideways" paints an unblinkingly funny portrait of the male ego in middle-aged disarray. But the harsh satirical edge that underlay "Citizen Ruth," "Election" and parts of "Schmidt" has given way to a more generous, forgiving spirit. The womanizing Jack may be infantile, but he's a likable monster. Whiny as well as winey, Miles is a first-class party pooper, but Giamatti takes us so deep inside his sad-sack psyche you can't help but root for his redemption. In "Sideways," Payne has created four of the most lived-in, indelible characters in recent American movies. This deliciously bittersweet movie makes magic out of the quotidian. And makes it look effortless.