The answer is that three things are obsessing them: the need to make buildings in ever more outré shapes, a slightly fetishistic preoccupation with that buzzword of the moment, "materiality"- meaning, what buildings are made of and feel like - and of course, what the destruction of the World Trade Centre portends.

There are good things at this Biennale, which is for once relatively straightforward in its aims. In the main exhibition in the gorgeous crumbling medieval naval buildings of the Arsenale, director Deyan Sudjic lays out big projects by all the fashionable international names, arranged by building type in a good, clear installation by minimalist John Pawson. There are real bits of big buildings by Jean Nouvel, Tadao Ando, Peter Zumthor, Peter Cook/Colin Fournier. There are huge models. All this is meant to show us what's going to happen in the world in the next ten years, because most of them are live projects. Hence the title of this biennale, "Next". What it does not show, because nobody knows, is what is going to happen next in terms of architectural movements. A crowd-pleasing section of skyscraper designs by more fashionable names - Zaha Hadid, Future Systems and so forth - is fun but does little to enlighten us on this matter. Sudjic describes this in disarmingly throwaway fashion as "the vulgar bit". Not at all: it provides an excellent midway point in the rhythm of the show

And then we have the other side of the Biennale - what individual nations choose to exhibit in their individual pavilions in the gardens set aside for the purpose a few hundred yards away from the Arsenale. The director has little power over what happens there. Although the national commissioners are meant to follow the main theme, most pay lip service only to it. There's a lot of the usual silly art-installation stuff, and floors covered with gravel, sand, rubble or - in the case of Austria - water. Banality follows banality.

An exception is the United States Pavilion, in front of which a twisted girder from the World Trade Centre is placed. Perhaps slightly too artfully placed. It looks like a Richard Deacon sculpture, overlaid with the characteristics of a piece of the True Cross. People queue up to touch it and to photograph themselves beside it. Despite this, it has immense power. Its sinister, ugly form speaks of hideous death.

Over the whole Biennale, the obsession with form - making buildings into funny shapes for the sake of it- looms larger than ever. With honourable exceptions, of course, such as the work of Brits such as David Chipperfield, Munkenbeck and Marshall and David Adjaye, or Ireland's Bucholz McEvoy and Grafton Architects. These people are making real buildings, not meringues. There are still right angles to be found.

It is a good architecture biennale in the sense that, in the Arsenale, Sudjic has dared to go mainstream, to be deliberately old-fashioned with real big bits of stuff, and not a video monitor to be seen. Apart from worries about manic form-making, the gossip at the show centred on the slight predictability of it all, and it is true there is a sense of boxes being ticked off as the modish names are brought into the fold one by one. There is the whiff of the fashion catwalk about it. Maybe it works on only one level - here's all this amazing stuff being built - but it works very well on that level, which is what matters.

You can ignore all this if you want. Every time I go to the Venice architecture Biennale, there is always one piece of enduring, pure architecture to be found. The 1962 Nordic Pavilion by Sverre Fehn looks better every time. A simple grillage of deep, super-thin white concrete beams, through which existing trees grow. A floating roof, with transparent sides. A massive angled corner. It is magnificent. It is pure, distilled architecture. So much so, that the exhibits placed in it are always comprehensively overlooked. Nothing can compete. It is far and away the best of the permanent Biennale buildings (and it is in the company of buildings by Rietveld, Scarpa, Hoffman, BBDO, Philip Cox, James Stirling and others). I'll go further. It is one of the best buildings in the world.

So the only images I'll show of Next, the 8th International Architecture Exhibition at the Venice Biennale, are of the forecourt of the American pavilion with its eloquently battered beam, and of Sverre Fehn's Nordic Pavilion, filled with light. Between them, they get to the root of what architecture is about.