The recent biennale was a big disappointment with one Irish visitor, noted for his diplomacy, describing it as 'a bit vacuous', writes Frank McDonald,Environment Editor.

AARON BETSKY did not endear himself to Irish architects four years ago when, on his first visit here (as an assessor for the AAI Awards), he suggested that they "borrow bits and pieces of the past, create fragments of civic grandeur abstracted to meet modern demands and never come together into a coherent and strong shape".

Betsky, who was born in Montana and now lives in Rotterdam, where he's director of the Netherlands Architecture Institute, will be remembered internationally for the travesty of his curatorship of the 11th Venice Architecture Biennale, Out There: Architecture Beyond Building, much of which is mere vacuous entertainment.

The Corderie of the Arsenale di Venezia, a 300m-long former rope-making factory that serves as the thematic core of every biennale, provided the backdrop for Ricky Burdett's magnificent presentation of the world's mega-cities in 2006. But now, as Gertrude Stein acidly observed of Oakland, California, "there's no there there".

According to Betsky's manifesto: "This biennale does not want to present buildings that are already in existence and can be enjoyed in real life. It does not want to propose abstract solutions to social problems, but wants to see if architecture, by experimenting on and in the real world, can offer some concrete forms or seductive images."

So what he's gone for is a sensory, even sensationalist presentation that includes a nude couple lounging on a mat in the middle of the Corderie. Otherwise, it is filled by swirling shapes, cool music, lighting tricks, toilet plumbing and seductive projections. The most fascinating exhibit was a map of Rome from the mid-18th century.

One Irish visitor, noted for his diplomatic skills, described the Arsenale exhibition as "a bit vacuous"; another characterised it more bluntly as "crap". Certainly, few were impressed by what was on offer, which appeared to have little to do with architecture - though the general public might get a kick out of it as a sensory experience.

Ireland took the biennale's theme more seriously in its exhibition of film-based work, The Lives of Spaces, at Palazzo Giustinian Lolin. In 2000, when we were first represented at an architecture biennale, Tom de Paor's peat briquette pavilion had a relatively remote location; now we're in the heart of Venice, right on the Grand Canal.

Housed in three sumptuous rooms, the exhibition tells visual stories, illuminating what some of our best architects do - such as Gerry Cahill's conversion of a former convent on Cork Street in Dublin into a social housing project, gathered around a copper beech planted many years ago by the Mercy nuns.

The most vivid of the presentations shows Gráinne Hassett's award-winning Brookfield Community Centre in Tallaght, a colourful contrast with its bleak setting, while the most evocative features Botharbui, home of Robin and Dorothy Walker on the Beara peninsula in west Cork, opening with a poem read by Seamus Heaney.

Grafton Architects watched films ranging from Kagemushato Mon Onclebefore commissioning Bang Bang Teo to make a movie juxtaposing two of their biggest projects, for Bocconi University in Milan and the Department of Finance in Dublin. The result so fuses the two projects that an old Milan tram seems to trundle along Merrion Row.

McCullough Mulvin's presentation of Waterford City Library has two figures in black standing motionless in every frame, to represent the architects, while Tom de Paor offers a quirky take on camera obscura to highlight a "picture palace" for Galway while O'Donnell + Tuomey show a superb cardboard model of their Gaeláras project in Derry.

Domesticity in Dublin, contrasting an old Victorian family home with a new house in the rear garden, is the focus of two young architects, Alice Casey and Cian Deegan of TAKA. But the most powerful punch is delivered by artist Dara McGrath's slide show documenting the demolition of the Maze prison; it evokes the dismantling of Dachau.

Directly across Campo San Vidal beside the Accademia bridge is the real star of this year's biennale, a stunning exhibition of the work and thought processes of Jørn Utzon, the visionary Danish architect chiefly known for the Sydney Opera House - perhaps the most important and certainly the most "iconic" building of the 20th century.

Now aged 90, Utzon lives in a beautiful house he designed in Mallorca, using local stone and brilliant light-filtering techniques.

The exhibition, magnificently produced by the Louisiana Museum, features a television interview with the architect.Utzon dismisses the notion that the opera house's trademark "shells" were based on orange segments as a simplistic way of illustrating its structural system. Instead, as he eloquently points out, it was inspired by cut-outs of the Earth's sphere and palm fronds; finding inspiration from nature was one of his strong points.

It would be great to bring this extraordinary exhibition, The Architect's Universe — Jørn Utzon, to Dublin. The only obstacle would be the cost, which could be as high as €100,000. Given his long-established interest in architecture and urban design - most recently in Ballsbridge - perhaps Dermot Desmond could do us a favour by sponsoring it.

The national pavilions in the Giardini are a mixed bag. Spain couldn't resist putting work by some of its best young architects on show. The French pavilion, which had been turned into a "commune" for the 2006 biennale, has a much more conventional exhibition this time - endorsed by a message of support from president Sarkozy.

The most arresting thing in the British pavilion was a series of graphics showing housing output in Europe, with Ireland way ahead of the pack at 19 new homes per 1,000 population (in 2004). Our housing was also among the most expensive, at just 3.35 square metres per €10,000 in outlay - exceeded only by greater London.

In France, the equivalent figure was 5.86 square metres and in Italy 4.1. The graphics also showed that we were getting very bad value for money, with an average room size of 16.7 square metres (just ahead of Britain at the bottom of the league table), compared to 29 square metres in Denmark, 26 in Austria and 23 in the Netherlands.

Scotland has its own pavilion for the first time - a timber structure, incorporating a broad flight of steps, designed by Gareth Hoskins and installed in front of Venice's Mussolini-era railway station. Called A Gathering Space, offering an opportunity to see the city from a new perspective, it was "supported by the Scottish government".

Back at the Giardini, the old Czechoslovak pavilion is nearly bare inside, apart from 15 identical fridges lined up against the rear wall, each one containing food for different households - a pensioner living alone, a student apartment, a family home, etc. But there's something prurient about opening them all.

The Belgian pavilion, dating from 1907, has been covered by sheeted scaffolding to mark its centenary, a year late, with a non-exhibition called After the Party. Plastic chairs are scattered around its bare rooms and the floor is covered by drifts of confetti. The intention was to "show it off in its purest form as a monument, empty and stripped".

Poland won the Golden Lion award for its entry, Hotel Polonia, with striking images of what some of its recent buildings might be used for in the future - including an overblown Catholic church turned into a leisure centre. More serene is the Nordic pavilion's retrospective of Norwegian architect Sverre Fehn, who designed it in 1962.

The lifetime achievement award went to Frank Gehry, who achieved celebrity status for his Guggenheim Museum in Bilbao; Aaron Betsky worked for him in the mid-1980s. But haven't we had enough of that drive by cities to acquire "icons" by starchitects - what former Winnipeg mayor Glenn Murray termed "irritable Bilbao syndrome"?

•• The Architectural Binennale runs until 23rd November