The combination of Johnny Depp and Al Pacino makes `Donnie Brasco' the best Mafia movie since `Goodfellas'
Five types of ambiguity: in the mouth of a Mafioso, the single phrase "Forget about it" can be used to signify (1) agreement (2) fierce disagreement (3) intense enthusiasm (4) violent rebuke, or it can simply serve as (5) a suggestion that voluntary amnesia might be a sensible career choice. Such semantic niceties are among the many lessons learned by the FBI undercover agent Joe Pistone (Johnny Depp) when he infiltrates the mob in the identity of a minor jewel fence, name of Donnie Brasco (18).

Pistone becomes the protege of Lefty (Al Pacino), a sour, frustrated hit-man who - Virgin to his Dante - shows the younger man not only how a wise guy talks, but how he dresses (no jeans), shaves (no moustaches) and drinks (no payments). Lefty's crash course in underworld etiquette helps make Mike Newell's excellent thriller the most anthropologically instructive study of mob life since Goodfellas. And it's the first to concentrate squarely on the penny-pinching ways of the Mafia's proletariat rather than the better homes and gardens of its bourgeoisie of aristocracy. Glamour? Forget about it.

Grasping that their basic story, essentially a true one derived from Pistone's autobiography, is tense and dense enough not to need any punching up, Newell and his talented screenwriter Paul Attanasio (a former film critic made good; cheers!) are for the most part content to let milieu and characters take precedence over action. Apart from a swift burst of garish sunlight when the action moves to Florida, the look of the film is cramped and grimy, and the pace is as watchful and measured as the BBC wildlife documentaries of which Lefty is fond.

When spasms of violence do burst on to the screen, they are all but unexpected and, rightly, all but unwatchable. About the most sickening moment comes when Joe aka Donnie joins his new buddies at a Japanese restaurant and is faced with the prospect of taking off his boots, thereby exposing the tape recorder he has concealed. With the ingenuity of despair, he contrives both an instant moral objection - he won't take orders from a goddam Nip - and a story to justify it: his dad was killed at Okinawa, leaving him an orphan. As alive to the minutiae of appropriate behaviour as a gang of Emily Posts, the mobsters duly beat the hapless head waiter to a pulp.

Like other points in the script, this episode neatly dovetails two ethical curiosities. Pistone may be the good guy, but to pursue his covert crusade he has to instigate and carry out actions which make him quite as bad as the bad guys, if not worse; he becomes Lefty's surrogate son, knowing all the while that his actions will probably mean the man's death. You can see Pistone's moral fibre coarsen scene by scene until he finally hits his wife (Anne Heche). Contrariwise, Lefty and co may be a repellent bunch of killers, but when it comes to solidarity and stoicism they make a better impression than the FBI, whose in-fighting, pettinesss and all- found slovenliness repeatedly endanger their man's skin.

Skilfully riding these paradoxes, Newell and Attanasio have come up with an almost unprecedently mature gangster film, by turns horrified and properly unimpressed, but free of priggishness.

They're handsomely served by their stars: Pacino, who stoops and shuffles and jiggles with bone-weary nerves, may never have been better than he is as Lefty - an act of penitence for his more swaggering criminal parts? - while Depp brings to the title role a dour solidity that's miles away from his usual neurotic boy-outsider tics. He plays Pistone as a man who, unable to let his real thoughts show on his face, progressively loses track of what they might be. In short, Donnie Brasco never seems to put a foot wrong - which is to say that if I had any reservations at all, I appear to have forgotten about them.

Liar Liar (12), which - o tempora, o mores - took several bejillion dollars at the US box office, is a stinker stinker. Blessed with a potentially meaty premise about a mendacious creep (viz, a lawyer) suddenly cursed for 24 hours with the inability to tell porkies, it throws away every occasion for playing ingenious games with the theme so as to allow its star, Jim Carrey, to do exactly what he has done with every other leading role to date: talk fast, gurn horribly, make silly noises and hurl himself around like a over-paid bendy toy. Some of this is amusing in a moronic sort of way, especially if you are five years old, like the lawyer's neglected son, who provides the film with its quota of sticky pathos. Too much of the humour is offensive, however, and not because it's about flatulance or enormous breasts, but because Carrey's performance shrieks with self- love. Its nearest approach to wit is a touch of the self-referentials. Not only is it untrue that pulling funny faces can deform you for life, the lawyer tells his boy, some people actually make a good living that way.

Self-referentiality is also the one big joke of another US hit, Wes Craven's Scream (18), a stalk-and-slash movie about a bunch of eminently sliceable teenagers who dote on stalk-and-slash movies such as Halloween, Friday the 13th and Craven's own Nightmare on Elm Street, and constantly make remarks along the lines of: "If this were a scary movie, I'd be the prime suspect" or, noting the incompetence of the police investigators, "If they'd watch Prom Night, they'd save time." If I'd paid for my ticket, I'd have felt cheated. Unless you have major ethical qualms about the S&S form, it's diverting enough, but like most navel-gazing jokes it rapidly begins to induce a sense of pointlessness. To adapt the old adage, Scream proves that the slasher film has passed from barbarism to decadence without an intervening phase of civilization, though it is, admittedly, hard to imagine what a civilised slasher movie might look like. The Silence of the Lambs, perhaps.

Two relatively low-key productions offer more delicate rewards. The Boy From Mercury (PG), a first feature by the Irish director Martin Duffy, is about a pre-pubescent Billy Liar (Hugh O'Conor, an engaging lad) who retreats from the unpleasantness of home (recently dead father) and school (bullies, pandy-batting monks) into a world of sci-fi fantasies largely shaped by his consumption of Flash Gordon serials at the Saturday morning rush. Calculatedly charming but not cloyingly so, it is a fund of sharply remembered period images from 1960, and several eccentric pleasures, including a brief appearance by the original Billy Liar, Tom Courtenay, who plays the boy's potty uncle.

Another period piece, Margaret's Museum (15), directed and co-written by Mort Ransen, is a sombrely picturesque film, much less conventional than it first appears, and wielding a gruesome sting at the end. Set in a dirty-poor mining community in Nova Scotia around the late 1940s, it follows the difficult marriage of a self-willed woman (Helena Bonham Carter) to a bagpipe-playing dreamer (Clive Russell). The splendid Kate Nelligan turns in a harshly comic performance as the bride's misery-guts mother, whose daily banter could out-gloom Schopenhauer at 40 paces, and Bonham Carter's raw acting here should be a smack in the eye for anyone who thought that she was only fit for popsies.

Ravenous for some good old-fashioned arsy-fartsy dream sequences like they used to make when knights errant played chess with Death? Hie thee without delays to Female Perversions (18), where you can feast on countless repetitions of a real corker, featuring a semi-draped woman (Tilda Swinton), a tightrope, assorted archetypal figures in masks and robes, and a swimming pool in the shape of a crucifix. Hmm, tasty. Boasting descent - matrilineal, of course - from a book of feminist psycho-analystic theorising spun from the figure of Emma Bovary, Susan Streitfeld's astonishingly dismal film is also reminiscent of a less well-known work by Flaubert, the short dictionary of idees recues spun off from his last novel, Bouvard et Pecuchet.

Its heroine, imaginatively called Eve, is a driven young lawyer who is hoping to be appointed judge, but finds the path to the bench littered with heavily underscored obstacles, including a kleptomaniac anthropologist sister (thesis topic: matriarchies), a distant but sinister father, a hypertrophied taste for sweeties, recurrent dream sequences about tightropes of mud women, and a compulsive need to shop for expensive lingerie and cosmetics. These scenes seethe with puritan disgust, since one of the film's burdens - for the benefit of the hard of thinking, it's spelled out in monosyllables by a minor character - is that Femininity is a Social Construct, and lipstick is therefore fascist. Thoughtful men will leave cinemas feeling ashamed.

Cinema details: Going Out, page 14.