Badger-skin headdress: Firebird, Rhebok, Badger and Hare 2008 by Marcus Coates

Part anarchic happening: Hermito's Children by Spartacus Chetwynd

For better or worse, if you want to know what is happening in art today, try this experiment. Take a cab from the Saatchi Gallery's excellent exhibition Unveiled: New Art from the Middle East to Millbank, where the fourth Tate Triennial has just opened. Though the distance is short, the journey will take you from the end of one cultural era to the beginning of another.

Each work of art in the Saatchi show is complete in itself and rooted in one time and one place. But the art in the Triennial is open-ended, formless, and refers to something outside itself. Walking through the show is like spending a few hours aimlessly surfing the net. A seemingly endless stream of politics, porn, science fiction, history, culture and science flows past you so fast that when you leave it is hard to say where you’ve been.

French curator Nicolas Bourriaud uses an exhibition that was originally intended as a survey of emerging artists in Great Britain to show long-established figures like Gustav Metzger alongside unknown artists who may or may not be British. He dubs this aesthetic “Altermodern” (alternative to both to Modernism and Postmodernism), but I’d have paid tribute to the French international aid organisation Médecins Sans Frontières and called it “Art without Borders”.

The star of this show is Indian Subodh Gupta. His Line of Control fills a rotunda in the Duveen Galleries from floor to ceiling with a mushroom cloud-shaped column of stainless-steel pots, pans and kitchen utensils in a work so visually powerful it gives you goose bumps. A “line of control” refers to the contested borders between disputed territories, which to any Indian means Kashmir, and the possibility that the conflict there might become the cause of a nuclear exchange. By making his atomic blast out of harmless implements that virtually every person both in Pakistan and India uses in everyday life, Gupta subverts (and therefore neutralises) the meaning of the mushroom shape – a sign for death as universally understood as the skull and crossbones.

Wonderful British artist Marcus Coates shows a film of a performance when, dressed in a blue-and-white tracksuit (the colours of the Israeli flag), and wearing a badger-skin headdress, with a stuffed rabbit sticking out of his shirt front, he pays a visit to the mayor of a small town in Israel. The poor mayor (who doesn’t speak English and uses a translator) patiently allows Coates to play the role of shaman or intermediary between the animal and human worlds. After the bird and animal noises comes a lecture ostensibly about the defensive tactics of the nesting plover but really about how countries that perceive themselves to be vulnerable react to danger. It’s funny like Louis Theroux, but apparently heartfelt and without the sneers.

For sheer energy, look at the wonderfully named Spartacus Chetwynd’s flickering wall of TV monitors all showing her parody of a TV soap opera entitled “Hermitos Children”. Shot with family and friends dressed up in home-made costumes, it features a female detective who is investigating the crimes of a sex-mad entrepreneur who is murdering female dancers. Part high-spirited performance and part anarchic happening, the whole thing is silly beyond words and teetered at times on the edge of porn – but once you start looking at it I defy you to tear yourself away.

I don’t have space to describe half of the artists I liked in this show, but I should also mention a few of the ones I didn’t. Charles Avery’s ongoing project The Islanders describes in words and in meticulous drawings a world of his own imagining both through visual art and the written word. In this show he exhibits a giant sculpted head of a fictitious dinosaur he calls the “Aleph”. The precedents of his work are as much literary (Gulliver’s Travels and Utopia) as visual and I think it appeals as much to science-fiction geeks as to the gallery-going public. I can’t say that Avery is a bad artist, but what you finally think of his work will largely depend on your tolerance for whimsy. I personally find the whole Islanders project insufferably twee and deeply tedious, but don’t let that put you off.

Too many artists – David Mellors, Olivia Plender, Shezad Dawood – were allowed to bang on and on without taking us anywhere in particular or giving us anything of interest to look at. I’m all for artistic self-indulgence, but in these cases I couldn’t find an ultimate purpose that made sitting through these lengthy performances worthwhile.

Still, the duds were offset by strong works by long-established names such as Mike Nelson, and Bob and Roberta Smith. Even as I left the show at the Saatchi Gallery, I knew I wouldn’t feel the need to go back. My experience of the Triennial wasn’t nearly as satisfying, but I’ll return again and again. How’s that for a back-handed compliment?