CANNES ON its 51st birthday is afflicted by a sense of morning after in the wake of last year's monumental half- century bender. The festival's very poster, butterfly-shaped shards of celluloid flapping through the sky, looks like something advertising a horror flick called Invasion of the Killer Bats - which would be light relief compared to some of the actual fare on view. Drug and alcohol abuse, madness, concentration camps, Stalinist purges: these are the subjects with which film-makers have seen fit to entertain us. Paedophilia and sodomy are the topics of choice (the latter even figures in Ingmar Bergman's new telefilm, In the Presence of a Clown) and there is a whole slew of movies about the end-of-millennium apocalypse. Fortunately - and this must reveal something about the current zeitgeist - a number of them are comedies.

The most bizarre is undoubtedly The Idiots, the new film from Lars Von Trier, the iconoclastic director of Breaking the Waves, about a commune of sane people who go round pretending to be mad. The film opens on a note of mocking, sometimes infantile humour as they stage various stunts to antagonise the surrounding community and fend off attempts to sell the house where the cult is based. But it takes a darker turn when some Down's Syndrome people visit, the group begins to fragment and some of the faux idiots become genuinely unhinged. Von Trier's scant regard for political correctness, plus a high penis count and an explicit shot of penetrative sex are just some of the reasons why The Idiots looks headed for a rough ride commercially. But this provocative, disturbing and unpredictable piece confirms its director as among the modern cinema's few true originals.

The Idiots is one of the first fruits of Dogma 95, a group of four Danish directors who have declared war on bourgeois cinema (whatever that means) and drawn up a back-to-basics manifesto in which they pledge to shoot only with a hand-held camera, natural light and direct sound, and without special effects or elaborate props. Absurdly prescriptive as this sounds, it appears to work, since the only two films produced under its aegis are both in competition in Cannes. The other is Thomas Vinterberg's The Celebration, about a spectacularly dysfunctional family gathering to fete their patriarch's 60th birthday. A bombshell is dropped when the eldest son rises for an after-dinner speech and, after a couple of congratulatory platitudes, reveals that he and his twin sister, who has recently committed suicide, were sexually abused by their father. An unsettling tone of black farce is established as the other guests attempt frantically to restore a mood of jollity.

In this film, however, the rough-edged Dogma 95 look is like a visual gimmick grafted on to what's essentially a routine yarn about a haunted family struggling to exorcise its demons.

The overall standard of entries is, by general agreement, strong - higher, certainly, than in previous years. But awards are an acutely political affair, a complex system of checks and balances, of apportioning favours evenly between America, France and the rest of the world, and of playing off art against Mammon. In 1997 the choice spoils were shared by Iran and Japan (Taste of Cherry and The Eel; neither has opened yet in Britain), and so one would expect this time to see Hollywood at the gates, but the US films in the official selections are a motley lot. The advertising campaign for Godzilla, the closing film, stands as some kind of touchstone for the unimpressive studio presence: "Bigger than the Carlton [Cannes's premier hotel]", is all it can find to commend its monster. "Size Does Matter." It was probably inevitable that some of the scuzzier market films would start flagging themselves as "Bigger than Godzilla". The biggest disappointment was Terry Gilliam's delirious version of Fear and Loathing in Las Vegas, an adaptation of Hunter S Thompson's novel which follows a drug-addled odyssey through the dark backwaters of Nixonian America. Complete with bald pate, Johnny Depp offers a hypnotic impersonation of Thompson, but the film is a chronically chaotic and indulgent suite of surreal vignettes which shed little light on the motives behind his descent into delirium, and appear to take the character's rampant misogyny at face value.

Of the US indies, the best-liked has been Hal Hartley's Henry Fool, a corrosive piece about a reclusive dustman who becomes a celebrity author overnight when his scatological poem is posted on the Internet. And, in the Directors' Fortnight, one film has made a real splash: Happiness, by Todd Solondz, the director of Welcome to the Dollhouse. His new effort is another excruciatingly comic excursion into suburban misery, sexual deviance and the increasingly elaborate ways people find to torture each other.

There is no real consensus on the competition leaders. The Italian actor- director Roberto Benigni has fielded the sentimental tale, Life Is Beautiful - yet another comedy - of a father who, incarcerated in a Nazi concentration camp, tries to pretend to his little son that they are, in fact, there on holiday. Ken Loach's My Name Is Joe - the highest profile picture among a conspicuously thin line-up of British entrants - has met with almost universal approval. It's a romantic comedy - a rare beast in the Loach oeuvre - about the shy and tentative love which grows between Joe, a recovering alcoholic, and a social worker, a relationship endangered where local mobsters blackmail Joe's best friend. It's a tender, beautifully judged film which reprises many of the director's abiding themes. And since Loach's last film in Cannes, Land and Freedom, won no prizes at all, despite being critically lauded, it seems unlikely he will leave again empty-handed.

The 'IoS' is holding a free screening of 'Taste of Cherry' (PG). See Going Out, page 11.