Howard Stern is a problem. It's easy to dismiss Jim Carrey as that guy who acts like a cretin for $20 million a throw, but Stern is the smart face of Dumb America, and this makes him impossible to ignore.

Private Parts (18) is a bizarre essay in auto-idolatory, based on the memoirs of America's top shock jock. Larry Flynt had the modesty merely to make a cameo appearance in his own hagiography; Cole Porter let Cary Grant flesh out his reasons for joining the French Foreign Legion. Here, Howard Stern stars as Howard Stern in the Howard Stern Story, moulding his own myth in the way that Eisenstein reconstructed the Potemkin mutiny, only with more fart jokes.

Although Stern and director Betty Thomas have created something that is at turns funny, repulsive and mystifying, this is a movie without any discernible purpose. Stylistically, it's a dog's breakfast show, aiming at a flavour somewhere between Radio Days, The Great Rock'n'Roll Swindle and Porky's II: early sequences during the Stern childhood ape the Allen confessional mode right down to the Brooklyn Bridge, the jazz soundtrack and the yammering father. Stern's ass-kicking at NBC radio recalls Malcolm McLaren's cocky claims to have fleeced the British music industry. The movie's nerdy impulses seem to preach that there's little in life more laudable than persuading some big-bosomed blonde out of her bra.

That the film is even interested in pushing in these first two directions makes it a more significant work than, say, Dumb and Dumber, and suggests something of Stern's complexity. He may have Steve Wright's moustache, Simon Bates's glasses and DLT's perm, but Stern has a Mephistophelean sophistication, too - as anyone who saw him kebab Chris Evans on TFI Friday will testify. Private Parts has similar bayonet action. For instance, Stern recreates a radio routine in which he claims to be a Vietnam vet, protesting that his blowing up a village of "gook children" didn't earn him enough kill-points. For a moment, he becomes the toughest satirist on the block, but the effect is short-lived. At home, when his wife Alison (Murder One's Mary McCormack) miscarries, Stern cheers her up with a bedtime gag about sending Polaroids of the expelled foetus to her mother. Implausibly, she finds this hilarious, only objecting when hubby repeats the routine on his show.

It's this scattergun outrageousness that exposes Stern as a man with no real critical project. He's closer to a Tourret's syndrome sufferer than an entertainer. And if there was no rationale behind the shock tactic the first time round, his motives for reconstructing these events with a combination of cronies and actors seem doubly opaque.

Stern excuses his humiliation of others by endlessly pointing up his own failings. "All I'm trying to do is be funny, and I end up feeling like an asshole," he opines, and, by way of self-deprecation, there are numerous references to his small penis. But let's face it, if he was being as honest as his film's title pretends, he'd have gone the whole hog and whopped it out on the mixing desk.

There's less coyness and more absurdity in Mira Nair's Kama Sutra: A Tale of Love (18), a two-dimensional melodrama set in 16th-century India and overstuffed with tantric T'n'A (tongues'n'anklets, in this case). When Maya (Indira Varma) seduces the dissolute Raj Singh (Naveen Andrews), she is forced to flee her home, and ends up taking love lessons at a sexual academy run by ex-royal courtesan Rasa Devi (Bollywood icon, Rekha). Rasa tells Maya that she's a natural at the job, and Nair spends much time demonstrating how some are born courtesans, some become courtesans, and some have courtesans thrust upon them. There's much thigh-kissing, nipple- munching and rolling around in the split peas, but despite cartloads of petals, gallons of oil and more incense than you could shake a joss- stick at, the ludicrous wins out over the sensuous at every take. The boom mike also makes a couple of unwelcome intrusions: this was either technical incompetence, or my misunderstanding of the finer points of position 342.

Marvin's Room (12) is so loaded up with terminal illness that it has as much nosology as narrative: there are paralysing strokes, mental illness, asphyxiation, leukaemia, senility and chronic back pain. Even the doctor's receptionist is on lithium. But above all, there's the Big C - Crying. Heavyweight emoters Meryl Streep and Diane Keaton play Lee and Bessie, two estranged sisters reunited by the latter's need for a bone-marrow transplant. Lee has her troubles, too, in the form of her sullen, unpredictable teenage son Hank (a smart, lucid performance from Leonardo DiCaprio). Between them, they produce more tears and snot than a six-pack of Juliet Stevensons. Through the seizures and the x-rays and the coughing up blood, it's sentimentality of a soapy but stirring sort, and Scott McPherson's screenplay (expanded from a stage hit), contains enough crooked humour to prevent matters becoming too maudlin. There's a stimulating shot of comedy from Robert De Niro as the tongue-tied Dr Wally, and broader farce from Gwen Verdon's Aunt Ruth, obsessed with a pair of good-or-evil twins on a daytime TV soap, and equipped with an electric "self-anaesthetiser" that causes the garage door to open every time it's operated.

The rest of this week's releases are in desperate need of a gag or two. Halfway through The Devil's Own (18), blue-eyed IRA boy Rory Devaney offers this bit of advice to conscience-stricken New Jersey cop Tom O'Meara (Harrison Ford): "Don't look for a happy ending, Tom. It's not an American story, it's an Irish one." If peace in Ireland depends on dialogue, let's hope it's not dialogue as terrible as this. Whilst Ford and Pitt do their best to cosh a bit of emotional conviction into a boneheaded script, not all of the cast are of the same mind. Simon Jones, best known for his dressing- gowned hero Arthur Dent in The Hitch-Hiker's Guide to the Galaxy, adds a welcome touch of Monty Python to his sneering SAS officer, with fruity delivery of lines like, "Harry Sloane, British Intelligence. I've been tracking down these murderous bastards for years."

The irony of The Devil's Own is that while it argues that the war in Ireland is too complex for outsiders to comprehend, it can only advance this argument in terms of crashing cliche and farcical improbability. This is how the plot works: Brad's father is shot in front of him as his Ma serves up Irish stew in their clifftop cottage, and so he joins the IRA - which seems to involve wearing a beard and a chunky sweater that make him look more like a member of the Kon-Tiki expedition than the paramilitaries. After an OK Corral-style shoot-out in Belfast, he escapes to New York to procure stinger missiles from a shady bar owner (Treat Williams) and ship them back home. No, I wasn't convinced either. Credibility is not helped by the Riverdance-style music that hijacks the soundtrack whenever Brad feels nostalgic about the old country.

With a release date neatly timed to coincide with the judgement passed on Timothy McVeigh, The Chamber (12) is a death-row drama of the sort that, by now, John Grisham's word processor could probably write on its own. Gene Hackman, his face like a hessian sack full of lemons, plays the white supremacist facing execution, Chris O'Donnell the young lawyer battling to secure his acquittal. Hackman grouches and snarls his way through Grisham's Pot Noodle of a narrative like a man condemned to speak two hours of clangingly obvious dialogue. O'Donnell, surely the most featureless leading man to emerge from Hollywood in recent years, is as boring here as he was in Richard Attenborough's In Love and War, helpless to do anything to match Hackman's cranky grand opera.

A long time ago, someone must have told O' Donnell that screen acting is all about looking from side to side with your mouth open. Consequently, every time he receives one of the plot's emotional shocks, he appears to be checking for oncoming traffic. He can hold his own against the similarly lightweight talents of Val Kilmer or Sandra Bullock, but here the boy don't stand a chance. In its favour, the film is less self-importantly lachrymose than last year's Dead Man Walking, and there's interest at the margins: outside the Mississippi State Penitentiary, Ku Klux Klan members protest against the death penalty while civil-rights activists parade with banners like "Gas His Ass". Ultimately, though, this is conveyor- belt stuff, as mass-produced as the Eskimo Pie ice creams that Hackman chooses as his last supper.

Cinema details: Going Out, page 15.