Art? It all boils down to a matter of taste

It's highly unlikely to go down well with dentists, but at the Serpentine you're positively encouraged to eat sweets. They're part of a Felix Gonzalez-Torres exhibit. Could this be the last word in interactive shows?

A long silver rectangle shimmers across the tiled floor, its surface crumpling into little waves of light, like an empty indoor swimming pool. Beyond, gauzy, blue curtains, drape the windows, edges lapping lazily against the ground. Breaking the stillness, a corner of fabric catches a faint breeze, and billows into the room, stroking the floor as it reaches in towards the silvery carpet, regular as breathing. A mirror on one wall faces a wall of pale canvases, veined with a tracery of hesitant lines. Tranquillity.

A long silver rectangle shimmers across the tiled floor, its surface crumpling into little waves of light, like an empty indoor swimming pool. Beyond, gauzy, blue curtains, drape the windows, edges lapping lazily against the ground. Breaking the stillness, a corner of fabric catches a faint breeze, and billows into the room, stroking the floor as it reaches in towards the silvery carpet, regular as breathing. A mirror on one wall faces a wall of pale canvases, veined with a tracery of hesitant lines. Tranquillity.

Around the gallery, the clicking of heels, as five sleekly-dressed women absorbed in their own thoughts, drink in the room. One by one they drop down to their knees, reach a hand into the pool of silver: a discreet rustling as they rise. The women do not appear to know each other, yet each seems to have fallen under the spell of the same choreographer. As each wanders the room separately, five lipsticked mouths dance the same masticatory dance, chewing up and down in polite, oblivious unison.

No longer just visitors, they have become participants in Felix Gonzalez-Torres's show. The shimmering lagoon, centrepiece of the Gonzalez-Torres retrospective at the Serpentine, is made entirely of sweeties. Chocolate-covered toffees, wrapped in silver cellophane. One imperial ton of them (kindly donated by Marks & Spencer), in an endless supply. Dip in, the artist invites, eat and enjoy, take my exhibition home with you, free.

Although the geometry of Gonzalez-Torres' s"candy spills" appear shaped by Minimalism, his sculptures carry none of the unyielding neutrality of a precision-made Carl Andre (do not try leaving the Tate with one of Andre's bricks in your handbag). Subverting the "don't touch 'til you've paid for it" dictum, Gonzalez-Torres not only confronts the notion of gallery as shrine, but burrows into our earliest taboos of never accepting sweets from a stranger. Least of all a queer one.

Born in Cuba in 1957, Felix Gonzalez-Torres died in Miami, from Aids in 1996. The candy spills, like most of his work, are a poignant reflection on mortality and the inevitability of transition and loss. Nothing is static. The ebbing piles of caramels, rehearse the death from Aids of Gonzalez-Torres' partner Ross in 1991, a life growing fainter day by day. In the mouths of his audience, the artwork ("Untitled" Placebo, 1991) is spread throughout the community, like a love-born disease, or perhaps its cure. A man might die, but memories of him live on in others.

Gonzalez-Torres left gallery curators free to choose whether to replace the candy as it is consumed, or to allow visitors to nibble away at the edges until the shape distorts, then disappears. The Serpentine have elected to refuel at the end of each day.

Elsewhere in the gallery, the sound of rolling paper, as visitors help themselves from tall stacks of printed paper. Huge red sheets with black borders or thick white cartridge bearing the alternative legends "nowhere better than here" and "somewhere better than here". Couples squabble gently over the best method of transportation. "No, do it like this, you're squashing it." "Take one," a Japanese couple coax their 6-year-old daughter. She looks down disdainfully. "Why?"

A string of bare lightbulbs forms a slightly forlorn square overhead ("Untitled" Arena, 1993). Is the party over? That's up to you. If you don't care to be wistful, take the walkman from the peg on the wall, reanimate the dancefloor, waltzing along to the Strauss on your earphones. "Play with it, please. Have fun. Give yourself that freedom," Gonzalez-Torres said of his art. "Put my creativity into question, minimise the preciousness of the piece."

A swoosh of beads, and a giant turquoise bead-curtain parts like the gateway to a tart's boudoir. A waterfall of bead rivulets to dance through, like Anita Ekberg luxuriating in the Trevi Fountain. A middle-aged man twirls a strand flamboyantly round his wife's neck like a boa; a mother revs up her pushchair and charges the curtain to her child's excited chuckles. A few tentatively approach, then retreat. A woman with a blue umbrella leans through and kisses her lover on the other side.

Next door, a baby-blue go-go dancing podium, studded with lightbulbs, stands empty. A goateed man with a briefcase reads the description on the title-card carefully and approaches a gallery attendant. "It says, materials wood, lightbulbs, acrylic paint and go-go dancer in silver lame bathing suit, sneakers and Walkman," he points out hopefully. But alas, the go-go dancer in his arse-hugging shorts only visits the gallery for five hip-thrusting minutes every day, at times of his own choosing. Life is full of disappointments. But there is always hope and the vaguest chance that the sexy boy will dance for you.

High above, a frieze of words and dates runs the full circumference of the dome which crowns the gallery. It is an unconventional self-portrait of the artist - an intimate chronicle of Gonzalez-Torres's life. In jumbled date-order, a shorthand account of significant moments in his own life criss-crosses with world events: Mother 1986, Bay of Pigs 1961, Paris 1985.

All of Gonzalez-Torres' works are "Untitled", sometimes with an explanatory parenthesis. He seems to distrust language, yet ironically he finds it the best medium for portraiture, for reaching into the life not usually on show. His commissioned portraits required his sitters to tell all - failures, encounters, achievements - then see their CVs laid bare around their living room picture rails. Yet language is slippery. Without knowledge of the individual, these fragments are poignantly indecipherable. Was 1985 a good time in Paris or bad? Like the dancerless platform, we can only guess.

To support the Serpentine show, additional works are displayed in Tube stations and high-street sites from Archway to Brixton - 12 billboards show a photograph of an empty bed, sheets rumpled, pillows still hollowed by the heads which once lay together, both lovers now gone. Strings of lights twine round Hampstead and Chelsea and Westminster Hospital.

To fill in a few of Gonzalez-Torres' biographical blanks, visit the V&A Printroom (5th floor, Henry Cole Wing), where you can leaf through an album compiled by his friend Jennifer Flay. His life or hers? It isn't always easy to tell. See snapshots of the artist with his Siamese cats, his collection of 1950s starburst wallclocks, the postcards he sent and the little messages of thanks, of fear, of sorrow. Green ink. Joined capitals. "Things are a little strange these days. Good and bad, always in extremes. But we will go on. We are strong and we have hunger for life, love, places, passion."

Serpentine Gallery, Kensington Gardens, London W2 (020 7298 1515) to 16 July