Has modern art lost its bottle?

I always say, if you're going to be any sort of critic, be an art critic: it's so much quicker. Consider. Reading a book can take ages. A film, a play, a concert: two and a half to three hours is a normal running time, and you have to stay to the end. But with an art exhibition, well, two and a half hours is the absolute outside limit. That's a very large or a very absorbing exhibition. And two hours - to be honest, one hour, or a bit less - is generally quite sufficient. Art is shorter. But when a show comes in at about 20 minutes, something is surely going wrong.

About 20 minutes is what it took me to get round Beck's Futures at the ICA. It is a new annual art prize, sponsored by the art-loving beer company, designed to bring on "a new generation of British art" (every year?). Ten artists have been shortlisted, some with a bit of a career already behind them. They were picked by a panel of judges that included Jane and Louise Wilson and Jarvis Cocker. There is work in all sorts of media - painting, video, photo, wall-decoration, object, drawing. It is an average-sized contemporary mixed show.

It is not that it offers a bad time - just a quick one. With about 20 minutes, you needn't miss anything or rush anything. Without actively dawdling, I don't think you could do it much slower. Sure, I could have spent longer immersed in Stephen Murphy's three-screen video projection of simulated falling snow - longer, that is, than half a minute. It was nice, but I felt I'd got the idea and the sensation: dreamy, virtual, natural loveliness. And I had a hunch that the swirling flecks of white on blue would continue indefinitely to swirl exactly as they had swirled during that half-minute, and would not be interrupted later by - say - the sudden appearance of a virtual yeti.

Or there's a series of photos by and of Hayley Newman, performing a series of casual-surreal "actions". The captions explain. She gives a lecture having had her mouth anaesthetised by a dentist. She sunbathes in a negative bikini (it exposes only the parts a bikini normally covers). She wears, in public, a pair of "crying" glasses that pump tears down her cheeks. She hides, motionless, in a bin-bag on the pavement, and when the dustmen arrive, she jumps out. The ideas are funny and kind of thoughtful. But they do not hold your mind for longer that it takes to grasp them.

Or take Chad McCail's strip-cartoon drawing of Genesis Chapters 2 + 3. McCail is certainly an original. He uses neat, neutral-but-friendly drawing styles - the kind you might find illustrating an information leaflet, say - and fills them with a content that's slightly too heavy or too weird, but the mixture never produces the straight irony you expect. Here, something near to a Mr Men style is used to tell the story of Adam and Eve (but they're quasi-robots, and God is a blue triangle with arms), and it's not just jokey. It leaves you with a rather odd feeling. It's interesting. But it doesn't ask for much more time than would a more conventional strip.

Now it's true that a kind of brevity is simply the dominant aesthetic at the moment. A lot of work now is "short" and aphoristic, in the sense that it involves the interplay of rather few elements. But that interplay - if well founded - can generate a response that is complex, delightful and entirely gripping. The short forms of contemporary art can sometimes produce deep and lasting satisfactions. But highly economical art has its risks. One is pretentiousness. Another is slightness. As Henry James observed after watching a puppet play: "Remarkable economy of means. And of effect." That, in the nicest possible way, is the rule here.

But in that case, the means had better really be economical. Elizabeth Wright, for instance, deals in scale-shifts, and if you look out of the window of the ICA's upper gallery, you'll see, parked in the car park, a green Mini, but a green Mini that is in fact 30 per cent too big. Yes, disorienting, because nicely judged. It's magnified just enough to register clearly, but you can imagine not noticing, too. It makes for a pleasantly bewildering minute. But when you think of the laboriousness of constructing or getting someone else to construct the thing, and compare it with the speed of the pay-off, it seems completely out of proportion. The ratio of production to consumption is that of the most elaborately gilded nibble. Hours of preparation; down at a gulp.

Laboured or tossed off: those are works that speak in the same terms as people who approach you in the street with a clipboard: this won't take a moment. The difference being that, as a visitor to an art gallery, you can be presumed to have some attention-time to spare. That was why you came, wasn't it? And I suppose the thing that's troubling me is not the works themselves, but rather my assumption that a gallery exhibition implies a more sustained claim on one's attention than is made here.

Surely these are works designed for more transitory forms of public exposure. In one case, that has happened. David Shrigley's left-field cartoons were, until recently, featured in The Independent on Sunday, and though the presentation wasn't quite right, they might have worked well enough in that context, or in some other publication at any rate. I agree, they do need a bit of free space around them. But gallery exhibition makes them too portentous.

That's only a partial solution, though. Some works, while they seem too transitory for the gallery, could hardly find another channel of distribution. Where else could Martin Boyce's three hanging neon tubes, each hanging in one of the three dimensions, and titled Untitled (After Rietveld), be shown? It seems a problem. This is art, alright. It demands an act of focused and reflective attention. But it's fast art. It's over in the twinkling of an eye.

Perhaps this is just too high-minded or too narrow an approach to galleries. Some are for dallying, some not. And there's no point pretending. I know perfectly well what the daytime scene is at the ICA. You don't go there to spend a long time in an exhibition. You go there to sit and drink and chat and Net in the café. You go there above all to mooch around the latest style mags and theory texts in the bookshop. And in the course of the visit you may expect to pass through the galleries, have your eye caught, your thinking tweaked, without being importunately detained.

The ICA is not alone, of course. Contemporary art venues are increasingly taking on the same emphasis. So it is not surprising that artists make work that answers to this burgeoning art-style-theory-shopping-leisure climate. And I'm not saying that it's the end of civilisation as we know it (that was ages ago). I'm just saying, if it goes on this way, then I can foresee a time when the art critic's job will become such a complete and obvious doss that people may actually start to notice.

Beck's Futures: ICA, The Mall, London SW1. Every day until 17 May. Admission £1.50, concs £1.20. Prize-winners announced 18 April. Show tours to Cornerhouse, Manchester, and CCA, Glasgow