It would be fair to say that measured restraint or delicate, whispered nuance have never held too much interest for Tom Wolfe as a writer. He likes his America extremely loud and incredibly close. Now, at 81, the most vivid literary huckster of our times seems more thrilled than ever to crank up his volume. Back to Blood often reads like a novel for the hard of hearing, megaphone meets ear trumpet. You hesitate to say it is a rage against the dying of the light, since, having invented this register 50 years ago in his wonderful pyrotechnic journalism, Wolfe has been writing in it pretty much ever since. Still, this book is certainly among the shoutiest  and just possibly the last  of his comic bullhorn broadsides against soft-spoken liberal pieties.

The novel is more than 700 pages long, though you guess about 100 of those are taken up with punctuation. To his familiar bulimia of exclamation marks, Wolfe gorges here unexpectedly on colons, often throwing in a couple of dozen at a time, just because he can. Even for seasoned Wolfe-readers it takes a little while to reacclimatise to the exclamatory style  like being woken up at three in the morning in a strange hotel room by a blaring shock-jock talk show. The opening paragraphs add a new contender to the author's personal top 10 of headbanging intros: a speedboat is ripping across the harbour in Miami, and the description and talk of the three cops on board is interrupted every half a dozen words by the repetitive SMACK of the hull on the water. It's a typically self-conscious reader's health warning: hold on tight, Wolfe loves to yell, theatrically grinning from the wheel above the frothy tumult of his sentences, it could be a wild ride.

I interviewed the author in his hushed and punctilious Manhattan apartment when he was setting out on the journey of this novel four years ago. He had not long returned from one of the first of his white-suited fact-finding missions to Florida and was full of excited talk of Miami's racial politics out of which Back to Blood would emerge. "I'm still convinced that if you went to live anywhere in this country for 30 days you would see sides of life you didn't think possible!" he suggested. His curiosity clearly remained on full-wattage in subsequent visits to Miami but for all his closely reported detail  the novel, as ever, takes great pride in its observation of the tribal fashions of his characters, the particular $29.99 CVS shades favoured by river police, or the slang of brattish yacht-partying thong-worshipping teens  Wolfe likes to work with big themes.

The high-rev engine of this book engages with the implications of the great migration of Cubans to America's southernmost metropolis, and the reversion of white "anglo" culture to a dwindling minority voice, drowned out also by robust African American and Haitian and incoming Russian inflections. This politically fraught recipe  which gives the insistent bloodlines of the title  is salted with sex, which is no great respecter of cultural divides and which drives the action forward.

From the large cast of characters on which Wolfe's eye lights  the city's Hispanic mayor, its black police chief, the wimpish and sweating editor of the desperate Miami Herald and the inevitable Russian oligarch  his narrative comes to focus on a particular young second generation Cuban emigré, Nestor Camacho. Comacho is a young cop who barely speaks a word of his parents' Spanish but nevertheless inhabits an America quite distinct from his "americanos" colleagues; it is a divide that begins with body-shape: his toned gym fitness contrasts with their walrus bulk. In two televised acts of adrenaline-pumped heroism, Camacho inadvertently succeeds in turning whole sections of the city against him. First, in rescuing  and arresting  a Cuban refugee from the top of the mast of a tall ship, he manages to alienate the entire Hispanic community, and second in apprehending a 300lb black crack dealer he risks inciting race riots when footage of their struggle is posted on YouTube.

Though Comacho is a more convincingly human Wolfe creation than most  you at least root for him to spring fully to life  you are never really persuaded that he is more than an intensively researched, brilliantly expressive caricature among many, another cartoon of wild and whirling interiority. His adventures are played for laughs and drama but the reactions to them feed into the author's long-standing agenda of making mischief out of political correctness. As in Bonfire of the Vanities, his stage-managed ethical dilemmas once again get somewhere near pressure points of American anxiety about multiculturalism. Almost every conversation and interaction is seen to be filtered subconsciously through racial sensitivity of one kind or another, though  in Wolfe's eyes  this is a reality that dare not speak its name. Into this minefield Nestor Camacho blunders courageously.

There is something ritualistic about Wolfe's return to these familiar satirical hunting grounds, first established in his skewering of "radical chic" in the 70s. The money and pretension of modern art, a pet subject since The Painted Word of 1975, gets another amusing going over, in particular in a long bravura scene at Miami-Basel art fair, where billionaires stampede blindly for schlocky Hirst and Koons lookalikes. He has more to say, too, about the packaging and corporatisation of teenage lust, the ostensible subject of his last novel I Am Charlotte Simmons. One strand of this book is concerned with a creepy TV psychiatrist at a porn-addiction clinic, though once again the authorial voice itself sometimes seems fixated by what Wolfe insists on referring to as the "mons veneris" of his female characters, (or sometimes the "lubricious mons pubis"). After the infamous "rutrutrutrutrut..." sex of Charlotte Simmons, however, Wolfe tends to keep himself out of the bedroom here.

Intimacy has never been his strong suit. He is, still, at his best in the thick of a crowd, a master of group dynamics, at once in breathless close-up and sudden wide-angle. You don't necessarily go to his writing any more for fresh truth about American life but you can still marvel  and laugh  at many of these scenes, full of expertly realised grotesques, and the sheer chest-thumping compulsion of language that tries to do them justice.

There was an interview with VS Naipaul a few years ago, where he spoke about his reluctance to call his new book a "novel". "If a novel is something that a person in public life does to show how much he or she knows about sex or shopping," he explained, then the word was "tainted".

Lurching through Tom Wolfe's 700-page new novel with its cast of porn-addicts, body-builders, art-collectors, suave oligarchs and foxy jebitas, all sizzling together under the Miami sun, I understood Naipaul's qualms. It isn't that Back to Blood is entirely about sex and shopping, or even that it is entirely bad. But between its pandering tackiness, and its polemical grandstanding on behalf of its own supposedly realist aesthetic (it starts out with a newspaper editor on his way to a restaurant called Balzac's, and devotes many pages to ridiculing non-representational art, that dreaded threat to mankind), it leaves you with the feeling that if this is what a novel is, then maybe it really is time to move on.

The aim, squarely Victorian, is to "do" Miami in full cross-section: vertically from city hall to the projects, and horizontally through the principle ethnicities and subcultures  Cubans, Haitians, Anglos, Russian billionaires, Jewish retirees.

There's a political storyline fuelled by the antics of a ripped young rooky cop, Nestor Camacho, who keeps inadvertantly triggering near-riots in various sectors of the population as his well-intentioned acts of derring-do  rescuing a would-be Cuban immigrant from the top of a mast; tackling an enormous African American crack dealer  are subjected to the warping media misrepresentation inevitable in a city where, as Wolfe would have it, "everybody hates everybody". The buttons here  race, immigration, drugs, gangs  are hot, and Wolfe pushes them frantically, but also perfunctorily, building his dramas with so little regard for plausibility it's hard to believe he really cares a damn about the issues themselves (certainly not in the sense that The Wire, for example, cared about Baltimore's). And beyond some touristic local colour ("somehow all the little bakeries and diners in Hialeah used only white bags") there's little indication he cares much about the physical textures of Miami either. At any rate, this aspect of the book falls completely flat.

Then there's a more anthropological storyline, having to do with art, sex and status, and rigged around the question of whether some abstract paintings endowed by a certain Sergei Korolyov to the city's new art museum, and allegedly worth $70m, are in fact fakes. The linchpin in this plot is Camacho's one-time girlfriend Magdalena, all curving lips and breasts and "perfect lissome legs", who dumps him to trade up, first to her celebrity sex-therapist boss Norm Lewis and then to Korolyov himself. Relentlessly mean-spirited as this piece of the plot is (its key image is a photo secretly taken by the manipulative Lewis, showing the herpes-measled genitalia of a rich patient he is currently exploiting for his high-society connections), its themes do at least seem closer to Wolfe's heart, and they produce some correspondingly livelier passages, particularly in the second half of the book.

The first half, however, is uniformly awful. There was a time when Wolfe's sharp eye and acid tongue seemed the perfect instruments for conveying the everlasting face-off between elite and street that generates so much of the theatre of American life. But in Back to Blood those instruments have largely been replaced by a megaphone.

Where he once dissected, he now merely amplifies. Italics, repetition, exclamation marks, screaming caps, have become his stylistic mainstays, supplemented by laboriously spelled-out sound effects and foreign accents. "He could just see the lubricants and spirochetes oozing into the crotches of their short short-shorts! Short short short-shorts! Sex! Sex! Sex! Sex! " goes a typical passage. Things aren't ugly, they're "uuuuuuug-lyyy". A man can't just laugh, he has to go: "AahhhuhwaaaAHHHHHock hock hock hock"  repeatedly. Then there's the gleefully in-your-face stereotyping: thuggish Russians, indignant Cubans, kvetching Jewish yentas; the flaccid emphasis of "He was a classic Americano  very proper-looking. Over-the-top proper"; the lazy tautology of people seeing even themselves as stereotypes: "He himself realised that Edward T Topping IV was white Anglo-Saxon Protestant to the maximum, to the point of satire". And there's the thought-bubble inner life of the characters (Wolfe has patented a surpassingly annoying typographic device for conveying this  six sets of colons either side of a character's private observation, ie: "::::::This place is a real piece of work!::::::"). No doubt all this is knowingly, deliberately, "mimetically" crass, but so what? That doesn't amount to insight or irony, just crassness squared.

Of course, you can forgive a book almost anything  clichés, bad jokes, even transcribed Russian accents ("Zey speak no Engleesh ")  if it takes you somewhere new and interesting. I can't claim Back to Blood does that, but about halfway through I noticed I wasn't writhing in quite such agony any more.

It's a little hard to account for this, but I think it's partly a matter of Wolfe's determination to give you your money's worth, whether you want it or not. Never one to risk a lull in the tempo, he contrives to build the book almost entirely out of climaxes and set-pieces. There's a floating orgy, a scene of billionaires mobbing each other at Art Basel in Miami, a skanky strip club episode, a lavish party being filmed for reality TV, any number of trips to fancy mansions and exclusive islands, and then all the cop business  the drug bust, live action rides on marine patrol boats, standoffs between the mayor and the chief of police  The scenes read more like sequences from Miami Vice or Lifestyles of the Rich and Famous than anything out of Balzac or Gogol (name-checked by another restaurant). But what they lack in literary quality they make up for in a kind of attritional persistence. It's a very American, full-on, quantity-based concept of entertainment (you find it at amusement parks and certain restaurant chains). The stuff just keeps coming at you, and after a while something in you accepts it as a form of plenitude, however ersatz, and you succumb  or half-succumb.

But it's also, more interestingly, a matter of the book's little kernel of real animus gradually revealing itself through the clutter of scattershot mockery. The two ingenues, Camacho and Magdalena, may be the official protagonists, but the governing sensibility is that of Lewis, the sex therapist. Simultaneously lecherous and revolted by the flesh, misanthropic and status-obsessed, contemptuous of Miami's glitterati while desperate to join them, he gives the book's fundamental moral incoherence  its prurient fascination with everything it purports to despise  a plausibly human face. We recognise this type of scrofuluous, self-regarding cynic, and we get a sneaky kick out of watching him in action, just as we do with Thersites in Troilus and Cressida.

His big scene, leering and sneering his way through a floating party at the Columbus Day Regatta, where nubile co-eds bump and grind under a porn movie projected gigantically on a sail, is too atrociously written ("THRUST the turgid crotch of his trunks in her buttocks RUT rut rut rut") to qualify seriously as the apocalyptic vision of "where Man is headed!" that it purports to be. But in some of the later, smaller episodes, especially the ones built around the art world, Lewis's presence inflames routine caricature into something more interestingly pathological. The billionaire "maggots" crawling all over the pornographic art on sale at Art Basel; the naked avant-gardiste whose show, De-fucked, consists of her pulling lengths of sausage out of her vagina, are not subtle (Michel Houellebecq's The Map and the Territory covered similar ground with incomparably greater intelligence) but they give off an authentic biliousness.

And that, finally, is what the book has to offer. Not a compelling portrait of a city. Not real satire, which requires some modicum of wit. Certainly not proof of the half-baked premise of tribal regression alluded to in its title: "it's back to blood! Religion is dying " No, if Back to Blood has anything going for it, it is a quality of unusually pure bile  an enraged loathing and envy for just about everything. It doesn't save the book, but it commands a certain grudging respect.

 James Lasdun's It's Beginning to Hurt is published by Vintage.