Adapting classics into comics seldom results in classic comics. Hundreds of them have been attempted since the 1940s and they just keep vanishing into oblivion while the original novels remain in print. In the last couple of years, we've seen graphic adaptations of Crime And Punishment (relocated, with mixed results, to Putin's Russia), Pride And Prejudice (a charmless Marvel production), The Picture of Dorian Gray (surprisingly decent), Moby-Dick (computer-slick), and two different unsatisfactory stabs at Dr Jekyll And Mr Hyde.

SelfMadeHero is the most ambitious new publisher in this field, having issued difficult works like The Master and Margarita and The Trial as well as a crowd-pleasing Sherlock Holmes series and teen-friendly Shakespeares. Ulysses is probably on their "to do" list, but in the meantime they bring us Joseph Conrad's Heart of Darkness.

Veteran author David Zane Mairowitz adapts the text, in collaboration with the young Swedish/Kenyan artist Catherine Anyango, a newcomer to the world of graphic novels. Anyango's rendering of the script  pencilled and digitally manipulated in shades of dark grey  begins with a sooty splotch on a none-too-clean background, identified in subsequent pages as a dot on a domino and/or a negative after-image of the sun. That sets up her aesthetic for the book as a whole: a murky monochrome vision; subliminal connections influenced by avant-garde cinema; surreal mismatches of scale that allude to colonialism's distortions of moral perspective.

The degree to which Conrad shared the colonial values of Marlow, the merchant seaman who travels deep into the Belgian Congo in search of the mysterious Mr Kurtz, has long been controversial. Mairowitz makes no distinction between author and protagonist. His introduction refers to opinions held by "Marlow (Conrad)", and Anyango's Marlow is drawn to resemble our Joseph in all his vulpine gravitas. Excerpts from notebooks Conrad kept on his own journey through Africa in 1890 are strewn throughout, as if to imply that Heart of Darkness is no more than a fictionalised version of this "Congo diary".

Undoubtedly the parallel texts are related, but it would have been wiser to quote solely from the diary, or solely from the fiction. Conrad's novella gradually infects the reader with 38,725 words of malarial potency; Mairowitz's choppy script makes do with maybe 3,000. Moreover, he converts Marlow's musings and summaries into direct speech, giving characters a stilted air they don't have in the original.

This expository staginess did no harm to The Trial, fitting in with Kafka's absurdist tone, but it sits oddly here. Even when Conrad's original text offers electrifying dialogue, such as in the encounter with Kurtz's crazed worshipper or the final scene with Kurtz's grief-stricken fiancee, the best lines are not used. It's especially odd that Marlow's habitual recourse to the word "nigger" is expunged, since the n-word is such an obvious short-cut to evoking the period (and provoking debate). Mairowitz's Belgian Congo, while bloody and unpredictable, stops well short of being the festering obscenity revealed by Conrad.

Visually, the book fares much better. Anyango is a gifted illustrator who has tackled the transition to comics with a measure of trepidation. Having publicly confessed her unease about the sacrifice of so much of Conrad's dense, luxurious prose, she tries to compensate for the loss by making the drawings more "rich" and "immersive". They are certainly labour-intensive, a marked contrast to the uncluttered simplicity of other SelfMadeHero offerings such as Crime And Punishment and A Picture of Dorian Gray.

But whether Anyango's industrious commitment gets her closer to the original is a moot question. A meditative rather than kinetic talent, she lacks the instincts of a natural storyteller and approaches each panel like a limited-edition print. Many of the images here could be exhibited  and deservedly admired  in an art gallery if stripped of the semi-transparent word balloons pasted somewhat timidly on their hermetic surface.

Indeed, much of the text adds so little to the artwork that the book might almost have worked better as a wordless collection of tableaux. Conrad's novel is not what you'd call pacy, but it has episodes where things seem to be moving forward, flashes of humour, and bursts of excitement. In Anyango's version, everything is narcoleptic, doused with a dense fog of charcoal.

This may sound like a disparagement of her work, but it's actually a recognition of what makes the book distinctive: a crepuscular expressionism that's Anyango's own. Her jungles and waterways stagnate in the gloom, as if enclosed in subterranean sewers and torture chambers. It may not be quite Conrad's hell, but it's hellishly creepy all the same, a world where darkness has dominion over all.

An impressive adaptation, then, pictorially at least. But as a whole, it suffers in comparison to two masterpieces in different media. One, inescapably, is Conrad's novel. The other is Francis Ford Coppola's film Apocalypse Now. That adaptation, too, diverged audaciously from Conrad's vision  more so than Mairowitz and Anyango's  but the moviemakers managed to produce a Heart Of Darkness that achieved far more than a distillation of dread. Apocalypse Now captures the thrill of colonialism as well as the horror, the tragic allure of dying empires and the testosterone-fuelled lunacy of next year's wars. This graphic novel  to its credit and to its detriment  confines itself to dark shadows and ghosts.

Michel Faber's latest book is The Fire Gospel (Canongate).

My huge enthusiasm for the graphic novels I write about here is going to make reviewing Self Made Hero's latest Eye Classic, an adaptation of Joseph Conrad's 1902 novella, Heart of Darkness, somewhat tricky. Will I sound unhinged if I crank it up a little? Perhaps. Oh, well. All I can tell you is that I am a complete evangelist for this book, which I consider to be quite magnificent. Although I haven't read Heart of Darkness for many years (since I was a student, in fact, and a rather less sceptical person than now), I vividly remember the way the story of Marlow and Kurtz and their Congo adventures worked its singular magic on me, and I had thought the experience would be impossible to repeat. But, no. Reading this adaptation in bed the other night, I felt both horrified and beguiled, just as before  and closing it, I worried, just a little, that I would not be able to sleep.

Plaudits must go to both adaptor and illustrator. David Zane Mairowitz, who was in charge of the text, had the subversive idea of incorporating extracts from Conrad's own Congo diaries into the story  a move which reminds one that the novelist's insights into European colonialism in Africa were literal as well as, if you like, literary (this is a point well made by the historian Adam Hochschild in his book King Leopold's Ghost, and my hunch is that Mairowitz just might have read it). But he also makes good, minimalist use of Marlow's haunting first-person narration: speech bubbles are kept to a minimum so that the reader is always with Marlow, seeing the terrifying banks of the river only through his eyes (and sometimes, neatly, through his binoculars).

Illustrator Catherine Anyango, meanwhile, has brought to life Conrad's nightmare journey far more successfully than the movie-makers who came before her; I'm certain that in the future, I will think of Heart of Darkness, and see only her drawings. Anyango has worked in sepia tones, and her sketches are cloudy not only with river mist but with foreboding. Every face is sunken of eye and hollow of cheek. Certain frames are truly terrifying: the moment when Marlow sees the human heads on sticks outside Kurtz's Inner Station; the scenes in which Kurtz breathes his horrible last; and, most spectacularly, those which depict not human beings but the jungle itself. In Anyango's hands, tree roots become tentacles, and the leaves of succulent plants, rapacious tongues. The jungle will soon have its revenge.Kurtz's spectacular hoard of ivory, meanwhile, towers over Marlow and the other men, piled so precipitously high that it creates only more darkness.

Every page is both extraordinary, and extraordinarily beautiful, and I urge you to go out and buy it, whether you've read Conrad or not. Either way, you will turn to him. This version of his story works superbly on its own terms, but it also serves as a delicious hors d'oeuvre, to be scoffed before you embark on the real thing.