Gondolas are optional

For most of the current century, Liverpool has given the impression of being a modestly sized city living inside the carapace of a much larger, grander one. Its post-industrial present is garlanded with the trappings of an imperial past, all those huge buildings erected during its heyday as a port. And, with all due respect to the Merseybeat, its cultural profile has not been all that it might. The revamping of the Albert Dock and the opening of the Liverpool Tate were moves towards change. Other events, including the annual John Moores Painting Prize and, latterly, the annual New Contemporaries exhibition, have also played their sporadic part.

Now, in the midst of a period of renewal, the city has embarked on a brave new venture with the inaugural Liverpool Biennial - the first such art event in Britain. The Biennial incorporates both John Moores 21 and New Contemporaries 99, as well as an ambitious multi-venue international exhibition, Trace, and a very lively fringe programme irreverently termed Tracey. It also usefully co-opts some of those grand architectural spaces. It's brave because it's a daunting organisational challenge and because it invites comparison with other, bigger, long-established biennials, such as Venice.

It also invites the question of whether the world needs another art biennial, as the existing ones get inexorably bigger and less manageable. Certainly, as biennials go, Liverpool is a minor one, which is no bad thing. Trace, clustered in a few centres and distributed throughout the city, is directly comparable to several recent EV+As in Limerick, even down to the circumstance of the provincial, western city taking on the challenge rather than the eastern capital - except, of course, that EV+A is organised on a budget that is minuscule in comparison.

The title Trace is intended to work on several levels. As curator Anthony Bond puts it, you have to trace the exhibition through the city, working your way from the old cathedral downwards towards the port and the Tate Gallery. But it also refers to his strategy of selection. With admirable clarity, he writes that he was looking for contemporary conceptual art that offers a "trace" of the real as a means of negotiating the "crisis in representation" in 20th century art.

He argues that, by expanding the available language for artists, allowing access to the myriad associations of any and all materials, objects and technologies, conceptual art broadens engagement with each member of the audience. More to the point, he suggests that conceptualism has transcended its narrow art world preserve, that it "can no longer be considered an avant-garde gesture", and allows art to "serve a genuinely social purpose".

Bond deserves much credit for providing his show with a clear framework, and also for the diversity of his choices. The easy option would have been to round up the usual suspects and impress everyone with a few big names. In the event, many of the names are not only not big but positively obscure, and none the worse for that. Still, it's by no means entirely clear that the exhibition proves his point. One obvious example of the social engagement he mentions is Stephen Willats's project with the inhabitants of a west London housing estate. It is essentially a documentary project and, while it is engrossing and does give a voice to people who are marginalised and alienated, the artist's ideas of organisation and presentation are frankly the least interesting part of it, and actually seem clumsy.

More successfully, Bond's piece de resistance, an installation of works by Colombian artist Doris Salcedo in the vast, soaring space of the Anglican Cathedral, is pretty much a sure thing and it is more or less conventionally sculptural. Salcedo's work addresses the plight of her compatriots who have become pawns, uprooted, bullied and murdered by both sides in a vicious power struggle. With echoes of Rachel Whiteread, she collides and merges items of ordinary furniture, wardrobes cupboards and chairs, and seals the openings with blank expanses of cement. In the hushed precincts of the cathedral, the atmosphere is eerie and disturbing, the slabs of furniture suggesting both lost domesticity and tombs. They are also, it must be said, a little overawed by their surroundings.

Video, particularly projected video, is ubiquitous. Eva Koch's projected video records people precariously traversing a narrow raised causeway while waves break against and occasionally over it. It is a haunting, fascinating image. Canadian artist Stan Douglas shows a typically sophisticated installation - not a new work - in which overlapping images and sounds drift in and out of synchronisation, rather didactically dramatising the differing visions of rival colonisers in Canada.

In Pierrick Sorin's multi-monitor video installation, individuals with disturbingly composite, collaged faces regard each other shiftily, with twitching nervous movements.

Photography is evident, though not as prevalent as you might expect. Germans Nine Fischer and Maroan El Sani's work is based on a terrific idea. They photographed by day various inauspicious-looking facades that are unofficial temporary nightclubs. Their idea was to do the same in Liverpool and show the results side by side. This they seem to have done, until you discover that they cheated. Sadly, they couldn't find any such venues in Liverpool, so they photographed likely-looked candidates instead, which rather undoes the counter-cultural frisson. Maruch Santiz Gomez from Chiapas started taking photographs when she took part in an education programme organised by her local church. Her direct, forceful images, with accompanying texts, very effectively record the sayings and superstitions of her community. The body, outside and in, is a recurrent subject. Nicola Costantino's window display of garments looks ordinary but seems on closer inspection to be made from human skin (latex, thankfully), complete with nipples and orifices. The viscera overflow in Adriana Varejao's strange works, in which bloody entrails spill out of ruptured blue tile facades.

Gynaecological nurse Liu Shihfen has created an installation in which a range of ambiguous organic fragments is laid out on surgical tables like body parts at an autopsy. Benin artist Romauld Hazoume's improvised masks are character sketches fashioned from found objects, and recall the quick-witted inventiveness of Picasso's Cubist sculptures - appropriately enough, given that he was directly inspired by African art.

Inevitably, some pieces do seem vacuous and overblown, including that by Annelies Straba (who has exhibited at the Douglas Hyde Gallery), whose elaborate slide and video installation delivers little. Igor and Svetlana Kopystiansky's anthropomorphic video of rubbish blowing through the streets of New York sounds promising in outline but never rises above the banal. Reinhard Mucha's installation addressing notions of memory and transit is physically elaborate but so incredibly slight it doesn't remotely warrant the considerable bother of putting it together. And Miroslaw Balka's vast, seven-metre-square soap platform is a wash-out. The problem with letting artists loose in a space is that they may not deliver the goods.

New Contemporaries 99 draws on work by recent graduates of British art schools. It's a good show that works best as a show. That is, considered piece by piece there's not much that's wildly exciting, but overall you get quite a good impression, the fruit of canny installation design. Again, video projectors, the art world's latest plaything, are everywhere. Twin images projected onto opposed screens is now a particularly popular format, with derivative variations from K.R. Buxey (girls screaming at a 1960s pop concert) and Julie Henry (opposing supporters at a football match).

Kenny McLeod's very straightforward video - on a monitor - is quietly impressive. Called Robbie Fraser it is a head-and-shoulders shot of McLeod reciting a series of confessional monologues, couched in the formulaic language of psycho-therapy, with accumulating inconsistencies. We gradually realise that the apparent intimacy of the language, while apparently telling us everything, actually tells us nothing.

Louise Spence's documentary photographs of Maddle Farm are excellent and underline how strong straight photography can be. Natasha Kidd's painting machine periodically dips a small canvas into a bath of liquid white pigment. Jane Fox and Nathaniel Mellors both gather lots of miscellaneous objects together and display them in heaps in the hit-and-miss manner of Jessica Stockhholder and Jason Rhodes.

There is just one Irish artist in John Moores 21. Blaise Drummond he acquits himself well. Designed as a showcase for painting, it is a terribly disappointing show, with a rather dispirited air about it.

Germaine Greer was one of the selectors, and she pulls no punches in noting her disappointment with the women who submitted work. Mind you, she's not particularly enthusiastic about the men either, but she allowed more of them in on the basis that at least they had a go. The substantial £25,000 overall prize went to an increasingly fashionable Dutch artist, Michael Raedecker, who uses thread as well as paint to make odd, slightly surreal landscapes that combine the qualities of computer simulation with little jolts of three-dimensional effects. Yet ultimately his work is slight and, on a large scale, over-extended, a measure of painting's limited agenda. The same could be said of another fashionable award winner, Jason Martin, who rakes a thick, uniform white surface to engender a slight spatial ambiguity. Much of the work on display engages with photography in a fairly inconsequential way. There is also a great deal of downbeat, workaday urban landscape. It's hard to believe that this rather lacklustre selection emerged from a submission of over 2,000 works. Can contemporary painting be so weak? Alexis Harding, who exhibits with the Rubicon, and veteran John Virtue, who makes black-and-white works based on landscape, both looked extremely strong in this company.

The Biennial is potentially important for Liverpool - readily accessible from this side of the Irish Sea - but it cannot, in itself, put the city on the art map. As with IMMA here, the hope must be that the Biennial will be a two-way process: it will bring artists and visitors to the city, but it will also stimulate local activity. The sheer energy and diversity of Tracey events suggests that the latter is a reasonable hope. Though in the end, like all events in the north of England, it has to contend with the London-centredness of the British art world.

The Liverpool Biennial, incorporating Trace at the Tate Gallery, Exchange Flags and assorted venues, New Contemporaries 99 at Exchange Flags, John Moores 21 at the Walker Art Gallery, and Tracey events at assorted venues, runs until Nov 7th. Maps and information are readily available at all venues