Few books can have proved quite as alluring and problematic to film-makers as Joseph Conrad's slim novella Heart of Darkness. Orson Welles firmly intended it to be his own cinematic debut, and made bizarre and ambitious preparations accordingly. (The same basic format would appear in his late, unproduced screenplay The Big Brass Ring.)

When Francis Coppola and the Movie Brats got their hands on the book it certainly made the screen, albeit transported to the Vietnam-Cambodia border as Martin Sheen's American captain hunts down a renegade colonel in an elaborate, hallucinogenic acid-odyssey. This insanity of war culminated in an audience splitting hour of Marlon Brando's half-assed philosophical mumblings. Still, Apocalypse Now is a classic. British director Nic Roeg's take on the legendary text is something else entirely.

This film is weighted down with familiar faces - a bug-eyed Patrick Ryecart, James Fox, Peter Vaughan, Michael Cronin - but the focus falls inevitably on its leads. As Marlowe the splendid British actor Tim Roth is fine. He is rather called upon, like Sheen, to react more than instigate, but placed alongside John Malkovich's Kurtz his becomes a performance of almost Shakespearean gravity.

Malkovich - "The horror! The horror!" - is rotten. Malkovich has generated a considerable body of film work over the years, but time and again turns in flat, characterless performances. As Kurtz, emoting from inside a net curtain, he leaves the viewer wondering why Roth would travel to the end of the street to find the man, let alone half-way across Africa. And if anyone knows quite what Iman is doing then that's one more than the film.

The real disappointment in all this though has to be Roeg. Certainly some of the blame has to be laid at the door of the film's cable origins. It would be unreasonable to expect quite the same innovative editing and extraordinary juxtapositions that litter, say, Eureka and Bad Timing, but at the same time you have to wonder why hire a film-maker like Roeg if you don't want what he does best. Occasionally - very occasionally - there are hints at the mind behind, but they provide scant reward. Can this really be the same man that made the luminous Don't Look Now?

Heart of Darkness ought to be a journey into magic and majesty (Coppola managed it, whatever the cost), but nothing of the sort raises its head in these frames. Paul J. Peters' design in perfunctory, and to add insult to injury Anthony Richmond's camerawork is harsh and over-lit. Belize is ugly rather than enigmatic. (Roeg, of course, shot the brilliant Masque of the Red Death for Corman; he knows better.) Stanley Myers' score (one of his last) does at least sometimes engage the audience when all else fails.

There were possibilities in the Conrad for more contemporary resonances, not least examining attitudes to the ivory trade that brings both men to the Dark Continent, but Benedict Fitzgerald's frankly boring screenplay is having none of it. Added to which, this is yet another film saddled with badly mishandled flashback structure: what kind of a danger is Roth in when he is sitting on a dock reciting it to us?

At Cannes this year it was announced that Roeg will script Empress Of All The Russias as Bob Guccione's belated soft and hard follow-up to the god-awful Caligula. With Cold Heaven barely seen, now this ugly, pointless exercise, just how much more tarnish can the crown of a bonafide genius stand?