Reader alert: the following is unpleasant. An identical pair of anamatronic sculptures of George W Bush are having anal sex with pigs in Hauser & Wirth's Savile Row gallery. The pigs are also gamely porking one another to riotous sound-effect squeals and the motorised wheeze of servo-powered pistons. The sculptures are beginning to look a teensy bit flayed. As you approach, the twin Bush sculptures swivel their heads and give you a Terminator stare, their pink silicon bodies still humping away. This isn't the first time LA artist Paul McCarthy has gone bestial, though repetition never killed any artist. You could call it rigour, or evidence of a one-track mind.

Going beyond taste is part of McCarthy's schtick. But whose eyes water now at the sight of McCarthy's giant butt-plugs, or the huge pendulous pair of testicles that dangle from a rickety wooden gibbet? They are mere incidents in a huge and inane raft of abused art materials and abandoned forms. McCarthy is nothing if not copious.

McCarthy himself, or rather his hairy, life-sized body-cast doppelganger, is enthroned in Hauser & Wirth's Piccadilly gallery, in front of rows of empty church pews. Pot-bellied and naked, he is a mute and impotent king, cable-tied to his chair and surrounded with painting supplies. This is the artist as fallen hero, sage and fool.

Repainted, blown-up photographs lean against the walls: Britney Spears and Paris Hilton, an upside-down Henry Fonda in a cowboy hat, a pornstar money-shot and an old Playboy cartoon. These are tawdry images for dismal times, emptied of shock or even surprise.

Once, in his hilarious and savage video Painter, McCarthy played a whining and infantile abstract expressionist, an overgrown baby dabbling in paint and screaming for money. Now he is both elevated and debased, sitting it out on a wooden stage. Down in the gallery's basement, there's a video running in which an assistant is having a go at the artist's replica with an electric carving-knife. Parody and mock yourself this much and you save the critic the job of complaint.

Occupying space after space with defaced heads, gooey residues and evidence of crimes against sculpted humanity, McCarthy's show fills every room of Hauser & Wirth's Piccadilly and Savile Row galleries. A black and tarry ship of fools looms under the plane trees of St James's Square, and he has a further show running concurrently in New York (above). McCarthy in his 60s has become reprehensibly respectable, and ever more repetitious as time wears on. One recent video installation is no more shocking than a beauty salon depilation promo.

This show often feels stretched, pumped-up and routine rather than genuinely violent and atavistic, the qualities I always liked in McCarthy's horrible and sometimes frightening world. Where do you go when you've already gone too far? McCarthy's self-portrait as king might well be a comment on his own artistic fate, and for that reason is the best thing here. Where once his art looked dangerous and subversive, rumbustious and bracingly obscene, his ever more strident antics now look tired, their bite gummy. This, more often than not, is the fate of an art of shocks. We get inured to it, as does its maker. What might become of the artist in late lyrical mode,when he gets beyond the pigs and the drool, the daily hump and grind of the big-career artist? Maybe McCarthy will sleep through it all, like the king in his dotage.