Two longtime friends set out on a voyage of discovery in the week before one of them gets married in Alexander Payne's frustratingly uneven and disappointing road movie. Payne, whose first two satirical movies ("Citizen Ruth," "Election") adopted a take-no-prisoners yet fair approach to their subjects, has matured as a filmmaker, even while allowing a smugness and condescension towards his characters to creep into his work (see also "About Schmidt"). That's not obvious at first, as the film settles into a pleasing, sharp groove, when pals Miles (Paul Giamatti) and Jack (Thomas Haden Church) set out on a tour of California's wine country just before Jack is to tie the knot. Miles, a failed novelist still obsessing over an ex-wife, is the wine expert, alternately pretentious and sympathetic. Jack is a happy-go-lucky sort who wants one last fling before matrimony. When they encounter two attractive women, a waitress (Virginia Madsen) who knows a lot about wine and a single mother who works in a winery (Sandra Oh), the men are forced to confront their dashed dreams and to ponder their own hopes for the future.

Much of "Sideways" is top-notch, with witty banter reminiscent of excellent films like "Diner" and "Wonder Boys." The film looks gorgeous, too, capturing the languorous rhythms of a laid-back excursion where the destination itself is not what's important. The actors, too, shine; Madsen's never had a role this good and Giamatti ("American Splendor") finds new depths to explore in what's becoming a patent on neurotic, nebbishy characters.

It's in the latter part of the film, however, that Payne's moral agenda becomes apparent. He won't extend generosity of characterization to Jack, who remains a superficial creation and, in fact, exists merely to make Miles look good in comparison. "Sideways" may end on a note of satisfaction about Miles' possible future but the film itself fails to satisfy. Starring Paul Giamatti, Thomas Haden Church, Virginia Madsen and Sandra Oh. Directed by Alexander Payne. Written by Alexander Payne and Jim Taylor. Produced by Michael London. A Fox Searchlight release. Drama. Rated R for language, some strong sexual content and nudity. Running time: 123 min