FICTION: PETER MURPHYreviews The Pale KingBy David Foster Wallace Hamish Hamilton, 547pp. £20

TALK TO ANY American creative-writing teacher and they’ll tell you that the late David Foster Wallace is the most imitated prose stylist on US campuses. Everybody wants to be Dave, they’ll say, but the problem is that Dave was a one-off, and a deeply troubled individual.

Troubled, like paranoid, is often a synonym for too aware. If Wallace’s creative antennae were sensitive to late-20th-century vapours and information overload, even his suicide, at the age of 46 in September 2008, following a two-decade struggle with depression, seemed emblematic of a wider global ennui.

His best-known work, the 1996 novel Infinite Jest, interrogated addiction, entertainment entropy and a sort of cosmic sadness over the span of its 1,000 pages. A friend and Wallace devotee once described it as part of a trilogy of "millencholic" masterpieces, the other two being Paul Thomas Anderson's film Magnoliaand Mercury Rev's album Deserter's Songs. This reader is not alone in proclaiming it the best novel he still hasn't finished.

With the exception of Good Old Neon, from Oblivion(2005), Wallace's short fiction could be cold and tricksy, but his journalism was achingly funny, endlessly digressive, compassionate and polymathical. The collections Consider the Lobster(2004) and A Supposedly Fun Thing I'll Never Do Again(1997) can be read in a day or two, and reread a month later. His essays on porn-movie awards, pleasure cruises, David Lynch and Dostoevsky combine modern philosophy and postmodern slapstick in a tone that is learned but informal and warm. Only Wallace could have made a dissertation on grammar ( Authority and American Usage) as compulsively readable as Le Carré.

The Pale Kingis his posthumously published and incomplete final work of fiction. Its editor, Michael Pietsch, assembled the novel from about 250 completed manuscript pages that Wallace had earmarked as a sample to secure an advance on the finished work, plus a plethora of notes, floppy disks and unpolished extra material. Set in an Internal Revenue Service regional examination centre in Peoria, Illinois, in 1985, many of the characters' beautifully constructed origin stories atrophy after a couple of hundred pages. This may be because it's an unfinished work or it may be because Wallace was illustrating a graph of slow soul death and corporeal deterioration: life starts out vivid and multicoloured, then you graduate and get a desk monkey's job, then you die. Such a book was always going to walk a fine line between depicting tedium and being tedious. One passage portrays a slow office day as a fluorescent-lit hell:

He imagined the clock’s second hand possessed awareness and knew that it was a second hand and that its job was to go around and around inside a circle of numbers forever at the same slow unvarying machinelike rate, going no place it hadn’t already been a million times before, and imagining the second hand was so awful that it made his breath catch in his throat and he looked quickly around to see if any of the examiners around him had heard it or were looking at him.

Be warned: substantial swathes of this book examine bite-your-knuckles monotony in prolonged and graphic detail. Expression and depression are diametrically opposed impulses, but the writing of such a book must have exerted an almighty drag on the author’s spiritual resources. Wallace devotees will no doubt venerate him as the brave knight venturing where others feared to tread, into the teeth of the great 21st-century malaise of bureaucracy and boredom. In a crucial scene a Jesuit substitute instructor delivers an end-of-term summation to a class of number-crunching candidates:

To retain care and scrupulosity about each detail from within the teeming wormball of data and rule and exception and contingency which constitutes real-world accounting – this is heroism . . . Routine, repetition, tedium, monotony, ephemeracy, inconsequence, abstraction, disorder, boredom, angst, ennui – these are the true hero’s enemies, and make no mistake, they are fiercesome indeed. For they are real.

In the absence of its author's shaping hand, The Pale Kingcould have been cut to two-thirds of its present length. But what a 300-page novel it would have been. The first 65 pages of The Pale Kingare stunning, alternating between high comedy and deep pathos. A boy called Stecyk grows up so noxiously goody-goody that he drives reasonable people to near-homicidal acts. Two young born-agains wrestle with an unwanted pregnancy, caught between the horns of abortion and a loveless marriage. A girl's trailer-park childhood is rendered as a Faulknerian nightmare. Then there are the car-crash set pieces: a man dies when his arm is caught in a subway train; a teacher has his thumb sliced off by a workshop bandsaw while demonstrating how a careless student might get his thumb sliced off by the workshop's bandsaw.

Here Wallace is untouchable, not least as a prose stylist. He operates according to a formula that obeys two fundamental principles: first, that if a writer extends a sentence past its normal lifespan, its multiple clauses conjoined with ands and commas, the sentence automatically assumes a sort of wry comedy value; and, second, that if that sentence is scuffed with conversational slang and purposefully ungainly syntax, it mimics the character's thought processes and simultaneously imparts complex ideas in a reader-friendly way. This long-line barnstorming/brainstorming plus subsequent scuffing echoes no one so much as Lester Bangs, an influence rarely mentioned in connection with Wallace. It is hard to imagine that a pop-culture aficionado and voracious reader such as Wallace wouldn't have wolfed down and metabolised Bangs's Psychotic Reactions and Carburetor Dungat some point.

But for all the gabba-gabba babble, perhaps the most powerful part of The Pale Kingis the opening word painting of rural Illinois, a soulful and ecstatically sad piece of work that suggests The Flaming Lips covering What a Wonderful World:

An arrow of starlings fired from the windbreak’s thatch. The glitter of dew that stays where it is and steams all day. A sunflower, four more, one bowed, and horses in the distance standing rigid and still as toys. All nodding. Electric sounds of insects at their business. Ale-coloured sunshine and pale sky and whorls of cirrus so high they cast no shadow. Insects all business all the time. Quartz and chert and schist and chondrite iron scabs in granite. Very old land. Look around you. The horizon trembling, shapeless. We are all of us brothers.

Rereading such passages, the reader wonders what Wallace’s life and work might have amounted to had he turned away from his generation’s golems and written about music or nature or anything that nourishes rather than nullifies the soul.

Peter Murphy is a novelist and journalist. His first novel, John the Revelator, was published by Faber and Faber in 2009