The most compelling scene in Fernando Meirelles' violent and much admired City of God comes as the favela drugs boss, Li'l Zé, decides to teach a lesson to a gang of local kids (the 'Runts') who are defying his authority by stealing within the favela boundaries. Cornering two of them, he taunts them with the choice of being shot in foot or hand, shoots both in the foot regardless, and then forces one of his own youthful recruits to choose which one he will kill to prove his loyalty. For just a moment, in the midst of a film of frenetic pace and constant violence, everything halts. Li'l Zé's hapless supporter swings the pistol from one to the other of the now snivelling children, until, on the edge of tears himself, terror forces him to shoot.

City of God It is a remarkably powerful moment, and it's worth considering why it works as well as it does. After all, for much of the rest of City of God the daily violence of life in the favela is about as viscerally disturbing as a pillow fight. So rapidly and flashily does the film's editing hurtle us past the countless deaths, that we barely have time to register their presence let alone entertain a moral or emotional response. They are — as so often in modern cinema — rendered impersonal by their spectacular treatment. Only in this scene do we actually have a chance to enter emotionally into the appalling logic of violence. The camera cuts between close-ups of the mutilated and terrified kids, a subjective shot down the arm holding the pistol wavering between them, Li'l Zé's howls of encouragement, and the agonised face of the killer-to-be. As each shot is held, deferring resolution, stretching out the experience, we are drawn yet further into his predicament, wanting it to be over yet caught up in its terrible dynamic.

There is a marked contrast between the style used here, inviting, even insisting on our involvement, and that of the rest of the film which opts for pace and excitement. City of God deploys a battery of techniques of camera-movement, cutting, and narrative dislocation which have become all too familiar in modern Hollywood action movies. Tarantino, The Matrix, a bit of Scorsese perhaps, all stirred together to produce a film which, unsurprisingly therefore, has been welcomed in Brazil as a sign that Brazilian cinema can now compete with Hollywood's best. But the price paid for that stylistic mimicry is that City of God never reaches its real potential. For beneath all the flashy technique there does lurk a kind of 'social realism': the hand-held camera, the detailing of environment and social world, suggest a film with ambitions to capture the unremitting capacity of brutal, violent circumstances to breed brutal, violent lives.

But that implication, while clearly present in the narrated events, is largely overwhelmed by stylistic flamboyance. What's more, in Brazil — or so I am assured by the Brazilian friend who saw the English sub-titled version with me — the distinctive style and speech patterns of the drug-dealers and hoodlums has given them some allure, helped make them the height of cool among sections of the young Brazilian audience. An important identification effect entirely lost, of course, on those of us relying on sub-titles and seeing the film more as foreign art-movie than Hollywood thriller.

At its heart, then, City of God fails to resolve a key tension faced by any film that engages frontally with violence. As so many recent films attest, movie violence is exciting, doubly so when it is clothed in technical excellence and reinforced by stylistic excess. But if it is to be anything more than incidental stimulation, then film-makers have to find ways of making us face up to both the horror of violence and the ambivalence of our own responses. They have to involve us as directly as possible. The classic case of that, of course, is Peckinpah's notorious Straw Dogs, now at last available for re-evaluation on DVD. Its climactic confrontation surely remains the most powerful extended treatment of violence in cinema. We experience it as overwhelmingly claustrophobic because, for its entire length, Peckinpah insistently drags us into the awful logic of the situation much as we are all too briefly drawn into the shooting of the Runts in City of God.

Having made us complicit in the dramatic and moral dynamics of the film's first two-thirds, the final section of Straw Dogs forces us to face the consequences. Though by modern standards there is little explicit bloodiness, the stretching of time through editing, and the sheer, ugly physicality of the fighting itself, leaves us with a commanding sense of the inescapable calculus of violence. You do not need to sympathise with Peckinpah's views to recognise that there is serious, moral engagement at work here.

That engagement is what is missing from City of God and, more worryingly, from the evocation of violence in the work of so many of Meirelles' popular American influences. The moralism of Peckinpah has given way to the shallow postmodern chic of Tarantino, and the world of violent cinema is much the worse for it.