THIS YEAR'S model isn't a model-type at all. Sandra Bullock, star of While You Were Sleeping (PG), and Hollywood flavour of the month ("the new Julia Roberts"), is the most unlikely sex symbol since Barbra Streisand. Bullock's features have a cartoonish exaggeration: generous nose, brimming lips, and a smile so wide it stretches her face into a gargoyle of glee. She is not exactly the girl next door - but an idealised version of her, with sparkling teeth and undentable self-confidence. Even her name sounds unstarry (Anna Mae Bullock wasn't showbiz enough for Tina Turner). But the hype, and $8m a movie, tells us she's a star. Her first leading role may tempt you to say: Bullocks to that.

While You Were Sleeping is a wafer-thin romantic comedy. Bullock plays an employee of the Chicago Transit Authority, a lonely single woman, who every day fantasises about the handsome yuppie (Peter Gallagher) who buys his train ticket from her. When he is mugged and falls on the track, she saves his life. A mix-up at the hospital leads to her being mistaken for the fiancee of the injured man (who has been left in a coma). Circumstances, too complicated and contrived to explain, prevent her from revealing what has really happened or extricating herself from the bosom of her "fiance's" family. And besides, she's fallen in love with his brother (Bill Pullman).

Bullock captures well the spinster's dowdy existence (which may be a double-edged compliment), while Gallagher's large, squabbling family brings out the best in her. She is great at a sort of coy embarrassment, averting her eyes and laughing breathlessly, as if trying to suppress her mirth or nerves. Her merriment lends weight to those who argue that film acting is largely a matter of personality. But at times it is as if the film itself is a jape for her: she seems to be laughing outside it, instead of in character. Her warmth is infectious, but I find it more winning in her television interviews. Her male co-stars hold the film together: the under-rated Pullman, who can goof without slipping out of character; and the always magnetically malicious Gallagher, who spends too much time comatose for the film's good. They are all stymied by the script, which lacks both wit and heart. Even the shameless, grand-standing one-liners and tear-jerking finales of Nora Ephron would be preferable to the sketchiness of While You Were Sleeping. Characters, such as Bullock's amusingly lecherous, fat Italian neighbour, flit in and out. Neither the writers, Daniel G Sullivan and Fredric Lebow, nor the director, Jon Turteltaub, seem sure whether the film is taking place in the real world or in fantasy land. When Bullock saves Gallagher from the train, she mugs and jokes, and rolls over with him three times, as if in a cartoon. And yet later we're supposed to share her angst. The exposition is slipshod too, as when Pullman mistakenly thinks that Bullock is having an affair with the Italian neighbour, and so gives her a test to check that she really knew his brother. Why would an act of infidelity lead him to suspect her identity to be false?

Pullman's ham-fisted inquisition, like the film as a whole, dimly echoes Mitchell Leisen's 1950 classic No Man of Her Own. There, Barbara Stanwyck, escaping her lover, tried on the engagement ring of a young woman travelling on the same train to meet her in-laws for the first time. The train crashes and when Stanwyck comes round, she is in bed surrounded by the woman's in-laws, who assume Stanwyck to be their daughter-in-law (who, in fact, died with their son, in the crash). As the days go by, Stanwyck starts to let slip her ignorance of her supposed husband. While You Were Sleeping turns this noir nightmare into a sunny romantic fantasy. Leisen's grim message was that we are always alone, even in marriage. Modern Hollywood gives that a reactionary twist. The re-make's message is that no one can flourish without family. There is no such thing as the individual.

With its insistently perky soundtrack, While You Were Sleeping plays more like a rock video than a movie. Sandra Bullock's undeniable, dazzling charm may make her the right sort of star for this new, debased type of film. But there are signs too that her bubbliness may soon burst.

When we watch a Jacques Rivette film we are unsure of the destination, but we know that the trip is going to be long-haul. Out One (1973) lasted 13 hours; his most recent, La Belle Noiseuse (1992), presented four hours of an artist painting a nude - as slow-moving yet fraught with drama as a game of chess. Now Jeanne La Pucelle (PG), in telling the story of Joan of Arc, spans four hours, which are divided into two parts: Les Batailles and Les Prisons. Yet this is an intimate epic, ostentatious in its avoidance of action or melodrama. Early in Part 1, Jeanne is discovered in an ecstatic trance by her friends in Vaucouleurs. They witness her ecstasy; but we do not. Rivette, halting the flow with curt sub-titles ("The evening of February 14, 1429"), dwells as much on the surrounding details of his cinematic canvas as its centre. A scene of characteristic understated beauty depicts soldiers on horseback crossing a snow-bound field. We get a sense of travel and time alien to the whizz-bang of most contemporary movies. Rivette's film has a calm, almost monastic rhythm.

Inevitably, this leads to longueurs. But the performance of Sandrine Bonnaire, as Jeanne, is so richly detailed that they are rare. If Sandra Bullock represents the Walt Disney school of acting, Sandrine Bonnaire is like a Dutch oil-painting, austere yet teeming with minute observation and intricate feeling. When she enters a room of inquisitors, pride, arrogance and a kind of transcendence are written over her face. Explaining her "voices", she is matter-of-fact ("St Michel was the first who came to me"), but preoccupied. There are sparks of joy, but they get subsumed by her blazing purpose. Yet she remains human, a naive country girl elevated beyond her social skills, impatient with distractions. Her eyes smoulder under the surface of her serenity.

Rivette shows us the deep sexism of the society that condemned Jeanne, but also its humility towards her. She seems to represent a ray of hope in the gloom of their Dark Ages. The film is unsentimental but moving - especially when Jeanne finally breaks - and swells to a stirring martial score by Jordi Savall. The savagery of Jeanne's oppressors is compounded by the stiff elegance of their condemnations, quoted in the original. It is a demanding film, but one that offers rich rewards.

Christian Vincent's La Separation (PG) is an even better example of the cinema of nuance. Daniel Auteuil and Isabelle Huppert play a couple, with a baby boy, whose marriage is disintegrating while she has an affair. We never see her lover, let alone the sex. The film is a series of skirmishes, ranging from a hand rejected in the dark of the cinema to full-fledged fisticuffs. The scenes are shards of a fractured relationship. Screen acting doesn't come much more subtle than this. Watch the expressions on the couple's faces as they speed along on his motorbike after another fractious evening. Auteuil has a look of strained exhilaration; Huppert is all sullen disdain. Despite the fact that she is in the wrong, Huppert never lets up from her haughty fury; Auteuil's famously fierce features are wounded and wary. In most scenes, one or other enters or leaves a room; their lives are gratingly out-of-synch. Vincent has managed to make a compelling drama out of frayed nerves rather than from grand passions.

The City of Lost Children (15) is Jean-Pierre Jeunet and Marc Caro's long-awaited follow-up to their garish black-farce debut, Delicatessen. The same grotesque invention roams even wider and wilder - a disembodied brain living in a tank, a sinister Siamese twin, a circus strongman - in a harbour-side world of gruesome greens and dingy browns, where a crazed inventor, unable to dream, kidnaps children and steals their nightmares. A toy bandsman clashing his cymbals, on a child's bedroom window shelf, becomes a running motif. But clashing symbols is nearer the mark. For all their visual panache, Jeunet and Caro have surrendered to surreal self-indulgence.

Cinema details: Review, page 68.