Friday's performance at the Barbican in London started late, had an unscheduled intermission and was forced to omit some of its theatrical effects.According to the Evening Standard, "the opera's magic proved sturdy enough that pauses... failed to break the spell".Part of the London 2012 festival, the production continues until 13 May.First staged in 1976, Einstein on the Beach is an abstract, plotless piece featuring music, dance and spoken text that, according to the Barbican, "breaks all of the rules of conventional opera".The current production, premiered in France in March, lasts five hours and is directed by original co-creator Robert Wilson.Wilson, 70, took to the stage himself on Friday to apologise for the delays and advise the audience to "fasten their seatbelts".At one point a musician on stage was heard to repeatedly request "more light", while at another stage a glass elevator appeared to have become stuck mid-air.A Barbican spokeswoman attributed the difficulties to "a mechanical failure in the flying system" and said two subsequent performances had taken place without a hitch.he Guardian's Andrew Clements said the opera seemed "rather old-fashioned" and that the technical problems "added to that sense of dated clunkiness".Yet he saluted the "commitment, unflagging concentration and energy" of the performances, the "tireless" dancing and the actors' "faultless" delivery."If you're looking for 'meaning', this is a monumentally boring show," wrote Michael Church in The Independent. "But if you just say yes, it's intermittently glorious."Yet the Daily Telegraph's Rupert Christiansen remained sceptical, describing the production as "banal", "interminable" and "flatulently pretentious in its willful opacity".In an interview with the BBC last week, Glass said the piece had been "avant-garde" and "tradition-breaking" in the 1970s and was "still cutting edge".His opera, the 75-year-old went on, comprises "a series of images and movements that are reflective of [Albert] Einstein's world".Friday's performance concluded 40 minutes later than scheduled but still drew a standing ovation and sustained applause.