Welcome to La-La Land. As portrayed in Willard Carroll's romantic ensemble, Playing By Heart, Los Angeles is a sexy, after-hours sort of place, a nocturne of cocktail jazz, hushed lighting, beautiful interiors, Hockney pools and open fires. You'd imagine the affluent, middle-class characters who inhabit the film to be mostly content, and who wouldn't be in this privileged, money-honeyed milieu? They are as far from the city of police helicopters, carjacking and smog as Los Angeles can possibly get, short of disguising itself altogether. There isn't even the glimmer of liberal guilt that Lawrence Kasdan allowed in his LA story, Grand Canyon; this film refuses to pay even lip service to "issues".

Fine by me: let's have more films that romanticise cities all out of proportion (Manhattan, Roman Holiday, The Moderns - name your favourite). Playing By Heart would like to seduce us, too, and within this handsome urban setting writer-director Carroll prompts his cast to brood and bellyache over a question which most audiences will find similarly congenial. Namely, what is this thing called love?

The cross-generational cast is led by Hannah (Gena Rowlands) and Paul (Sean Connery), a couple who are approaching their 40th anniversary but are currently at odds over a near-fling he had 25 years ago. Meredith (Gillian Anderson) is an uptight theatre director who can't help being prickly even when she's being romanced by nice guy Trent (Jon Stewart); Hugh (Dennis Quaid) tells elaborate lies to strangers in bars; Gracie (Madeleine Stowe) and Roger (Anthony Edwards) get their extramarital kicks in hotel bedrooms; Mildred (Ellen Burstyn) keeps watch over her son Mark (Jay Mohr) as he struggles towards death from Aids.

This is already a pretty crowded plot and we haven't even got to Joan (Angelina Jolie), a flaky wild-child who's intrigued by sullen disco boy Keenan (Ryan Phillippe). She likes to quote this bon mot on the pursuit of love: "Talking about love is like dancing about architecture." The writer likes the line, too, so much that it's repeated not once but twice, which considering it's rather an old line seems excessive.

But then everybody else in this film talks in the same arch, duelling sort of way, as if they're expecting to hear their polished chat admiringly quoted back to them. Following yet another of Joan's self-absorbed monologues, Keenan is finally driven to explain why they might not be suited to one another: "I just don't come out with my whole life story over Martinis and a Coke." It's just about the kindest way of telling her she's a garrulous bore.

Yet his admonition, far from reining in the film's talkiness, seems to encourage a positive gab-fest. It's almost as if Willard Carroll believes that there is no romantic impasse which cannot be solved by people yammering on.

Some handle the script's fussy elaboration better than others: Gena Rowlands and Sean Connery make their bickering look as natural as, well, a couple 40 years into marriage. Rowlands does a wonderful job of suggesting a woman who's still surprised to find herself flying off the handle - the opposite of the professional poise she masters in her Martha Stewart-style TV cookery programme. That other old trouper, Ellen Burstyn, is also terrific as the grief-stricken mother putting a brave face on her son's agonising decline. Her face as she chokes back tears is more eloquent than any of Carroll's glib backchat.

The younger members of the cast are less engaging, their hard- luck stories sounding a little over-rehearsed. When Gillian Anderson, at her most emotionally constipated here, tells her suitor, "I don't want all this calculated artificiality", I had to laugh - you're in the wrong movie, honey. "Calculated" is precisely how this material plays, and it puts you on guard: it's the sound of people who mean themselves to be overheard.

In this way, it's quite the reverse of Robert Altman's Short Cuts, with which Playing By Heart has been compared. While one suspects that Altman's style isn't quite as freewheeling and improvisational as he likes to make out, the rough edges and desultory, off-the-cuff dialogue do convey the impression of something happening there and then; of the eccentric, hilarious and desperate nature of human interaction. Carroll's movie, on the other hand, feels like a high-toned soap opera that's been neatly concertinaed into a two-hour package, its disparate strands tied up in a bright bow.

Beautifully shot by cinematographer Vilmos Zsigmond, and scored by 007 composer John Barry, its picture of LA is affectionate and forgiving, and for most of the time lulls you into a glazed trance. But it's not a satisfying movie. Carroll hasn't Altman's sly, sidelong wit - not many directors have - and you long for something a little more risky and offbeat. Casting comedian Jon Stewart helps a little; his line readings still have a natural snap to them which "serious" actors tend to lose. He also gets a great Woody Allenish moment with an outsize dog.

For the rest, however, it's a case of which couple can outdo the other in psychobabble, used here as the all-purpose romantic balm. I thought Sean Connery had clinched it when he explained how "My love for somebody else made me love you more". But for sheer baloney, Ryan Phillippe's emotional volte-face should take the biscuit. "I can't wait to hear the next words out of your mouth," he tells Joan, the same woman he earlier berated for blurting out her life-story over Martinis. What happened there? Sounds like the writer lacks even the courage of somebody else's convictions.