Amid the critical outcry that routinely accompanies Bret Easton Ellis's novels, one thing rarely gets noticed: that the heartless violence, depraved sex and avalanches' worth of cocaine are mere sideshows to one main attraction: Ellis's favourite subject, by some distance, is himself. From 18-year-old Clay in Less Than Zero to the cynical, disoriented protagonists of The Rules of Attraction, Glamorama and, notoriously, American Psycho, Ellis writes most about what he knows best. As "Bret Easton Ellis", the anti-hero of Ellis's latest novel, Lunar Park, muses: "I could never be as honest about myself in a piece of non-fiction as I could in any of my novels."

The Daily Telegraph's Saturday magazine recently took him at his word, publishing six double-sized pages of what it described as "the prologue to his new novel, Lunar Park", under the headline "Bret Easton Ellis comes clean". The text was accompanied by (genuine) photographs of Ellis partying in New York, reading from his books, and accompanied by a woman the caption identified as "his ex-wife Jayne Dennis, the mother of his son Robby". According to the text, Bret, burnt out after years of yuppie excess, had recently moved to "nameless suburbia" with Dennis, an A-list actress with whom he had, 11 years previously, fathered a son. A series of bizarre and horrifying events had ensued.

The only problem? Jayne Dennis is an entirely fictional character, though Ellis's relentless publicists at Knopf have created a website - www.jaynedennis.com - dedicated to the faux starlet. The Telegraph Magazine's decision to publish a fictional narrative (including a mildly sensational anecdote about Keanu Reeves) as if it were a memoir is a measure of the hold that Bret Easton Ellis the celebrity has on the public imagination, which is equalled only by the hold that Bret Easton Ellis has on his own imagination. A good third of the characters in Lunar Park are refractions and reflections of Ellis and his previous alter egos. Take Clayton, an unfortunate whom the exigencies of Ellis's plot force to resemble Less Than Zero's Clay; Christian Bale (who, we are reminded, played Patrick Bateman in the film adaptation of American Psycho); a 20-year-old Bret; Bret's father; and Bret's son. Even the demonic soft toy, Terby, that Bret buys for his stepdaughter is a mirror image of himself: "Ybret" or, as he puts it, "Why, Bret?" This is a decent question: despite the atmosphere of heavy psychological revelation, it is difficult to unravel the significance of Lunar Park's doppelganger parade. Terby, for example, is last seen disappearing into the anus of the family Golden Retriever; it's anyone's guess what this says about Ellis's identity crisis.

Fortunately, amid the psychologising and the gratuitous references to Hamlet ("Fortinbras Mall" and "Osric Motel", anyone?), there are some entertaining interludes. The novel opens with a swift overview of Bret's - and Ellis's - career, from Less Than Zero to Bret's new "literary pornography" novel, Teenage Pussy. Ellis offers clean, pacy and fascinating descriptions of the genesis of his novels: Less Than Zero was written "quickly in an eight-week crystal meth binge on the floor of my bedroom in LA"; American Psycho, disturbingly, "wanted to be written by someone else".

Ellis has lost none of his talent for capturing the signs of the times with precision and wit. The incantatory lists of consumer goods in American Psycho, the knowing hipster banter and the epoch-defining single details - such as the moment in Glamorama when "1979" by the Smashing Pumpkins comes on the stereo at a New York party - all resurface in Lunar Park. He is still very funny on contemporary mores: this time round, the gnawing anxieties of affluent suburbia. "I actually heard the word 'portal' used as a metaphor for 'nursery school'," groans Bret.

As American Psycho's yuppie Manhattanites have given way to aspirational parents, the lists of celebrities and designer labels have been largely replaced by cabinet upon cabinet full of "meds" for adults, children and even the family dog (before its terminal encounter with Terby). The whole of Elsinore Lane is hooked on Xanax, Clomicalm, Super Vicodin, Klon-opin, Viagra, Prozac, Levitra, Cialis, Ambien, Ritalin and Adderall.

With all these chemicals washing about, it is possible to dismiss, as his wife does, the haunted-house happenings of Lunar Park as figments of Bret's unreliable imagination. The novel is also an over-the-top horror story (there's a copy-cat killer, a psychic detective, and lots of italics and one-sentence paragraphs) in the high-trash tradition of Stephen King.

Diverting as this is, Ellis is simply trying to do too much. The spooky stuff does not jell with his maunderings about fathers and sons, or his ruthless dissection of his own persona and career. Lunar Park ends up resembling one of the mutilated squirrels Terby is fond of leaving next to Bret's Olympic-size swimming pool: still bright-eyed and bushy-tailed, but with its guts in a terrible mess.

Rachel Aspden is deputy arts and books editor of the NS