Premiered at the opening of the Kennedy Center in Washington in 1971, Leonard Bernstein's Mass was commissioned by Jackie Onassis in memory of her first husband, John F Kennedy. President Nixon avoided the performance, advised that Bernstein's work might contain anti-war messages. Nearly 40 years on, Mass is still heavily redolent of the time of its creation, something emphasised in Jude Kelly's epic production by the images regularly thrown up on screen: political icons, flower power and the Vietnam war all figured prominently. Indelibly nostalgic, it also exudes the unmistakably fading fragrance of a period piece.

The closing event of the Southbank Centre's nine-month Bernstein Project, Mass had everything conceivable thrown at it. More than 500 performers took part, with young musicians from Brazil, Iraq, the US and the UK, including members of the National Youth Orchestra. Various children's and adult choruses participated, as well as a troupe of dancers and even a marching band. Under the careful baton of Marin Alsop, the feelgood factor was stratospheric.

Yet the work itself remains irredeemably mediocre. The perilous concept of a celebrant of the Mass who loses his faith halfway through, smashing up the altar before engaging in a full-scale mad scene, might have worked with better lyrics than Bernstein and his co-writer Stephen Schwartz provided, while the composer's eclecticism could have been used as an advantage had his inspiration on this occasion equalled his pretension.

But much of the score sounds like material that would have been swiftly removed from a musical by any self-respecting producer well before it hit Broadway. It remains a paradox that the composer of a work of genius like West Side Story should have plummeted so low while aiming so ambitiously high.