Ocean Belfast Festival
Poignantly billed as Merce Cunningham's last collaboration with John Cage, this large, peculiar, part-aleatory artefact (whose first staging, in 1994, Cage did not live to see) was developed from a set of "starting conditions" laid down by the composer before his death: the title, 90- minute duration and in-the-round floor plan (with the audience ringed by the orchestra), and a sound-bank of Cage's ideas, developed and finished by Andrew Culver.

Big as it is (15 dancers, 112 musicians), Ocean looks a little swamped in the vast Waterfront Hall, the circular dance floor, overhung by gargantuan lighting gantries, looking rather remote from the terraces. Even had this not been so, the slow elaborations and overlapping phrases of Cunningham's choreography (created with the aid of a computer program called Lifeforms) has a dreamy, abstract, even minimalist hue, almost ambient in the way it unfolds.

This sense was heavily reinforced by Cage's music. Perched in small bunches in the farthest-flung nooks and crannies of the hall, the orchestra (made up of local students) had to cope with "32,067 musical events" - sequences of short pieces played asynchronously without either score or conductor. The result, if half randomised, is far from cacophonous. Instead, it resolves into a diffuse and not altogether discordant drone, punctuated by the odd barp of a horn or timpani crash, and overlaid with the sometimes lewd- sounding comments of David Tudor's electronically treated undersea noises and whale moans. It's all pitched at a kind of atmospheric, suspenseful expectancy - although, after 20 minutes, you realise you're getting nowhere fast.

Against this rhythmically formless backdrop, the dancers work to their own interior clocks. Clad in body suits that accentuate the gauzy overhead lighting, they introduce themselves in overlapping solos and duets with long phrases of movement broken by held poses, often pirouetting and wheeling around the circular stage, before draining off the floor down the four exit pathways.

Somewhere between Martha Graham and Tai Chi, there is far more elegance than emotion to the choreography. Even in the duets, the dancers are ultimately immersed in their own worlds. The overall picture only really kicks in after an hour with the big group displays, each dancer starting his or her phrase a couple of beats behind the last, serving up eye-dazzling shoals of complex movement.

Given Ocean's largely eventless evolution, it helps to get your metabolic rate right down: if you're at all anxious, the clock-counter, displayed on an array of video monitors, is maddeningly unhelpful. That said, I was astonished at the warmth of the crowd's response. And when the septuagenarian Cunningham hobbled on, looking small and footsore on his arthritic ankles, they showered him with whoops of appreciation. It seemed he couldn't get off the stage after that: an utter tramp for the limelight, milking it with give-it-to-me flaps of his huge hands.

Last perf tonight, 7.45pm Waterfront Hall ( 01232-334400)