The hippie dream has faded in this musical revival.

Gielgud Theatre, London W1

The truism that if you can remember the Sixties, you weren't there, does not apply to Hair. Most people will have seen the 1967 hit musical at least as sober as I was last week, which makes its longevity all the more surprising, as this West End import confirms what must always have been the suspicion: to enjoy it properly, you would need to be high on something.

Gerome Ragni and James Rado's musical still has quite a lot going for it. First, it can boast three great songs, "Aquarius", "Good Morning Starshine" and "Let the Sun Shine In", plus what might be called a novelty track named "Sodomy", whose lyrics make up for the lack of tune. That's three or four more than many musicals. Back in the day, it also had shock value: reaching the London stage the day after the abolition of the Lord Chamberlain's censorship prerogative, there was full-frontal nudity and liberal use of the f-word. It also broke the fourth wall at a time when the proscenium arch was still sturdy. The tribe, as the chorus is called, pours into the auditorium; at the end, the audience is invited up to groove with the actors on stage. But none of these would have meant much if its theme did not celebrate the mood of the time: a general rejection of the mores of the elder generation and a deep political revulsion at US involvement in the Vietnam war.

This production is no ironic commentary on Hair and its era. At one point a middle-aged couple appear on stage announcing themselves as visitors from another generation. So are we today, but neither they nor we come to scoff and we are certainly given no encouragement to do so by the cast, which keeps rigorously in period. But this revival's fidelity to its origins is also its downfall, as one quickly sees what a mess the whole thing was. Subplots briefly launch, but fizzle out. The central paradox that signing up to free love does not abolish jealousy and possessiveness is addressed in one scene and hardly mentioned again. The main story - about Claude, a lad from Flushing, Queens, who is for some reason much taken with Manchester, and his call-up to the army - is fitfully told. The second act largely abandons narrative in favour of a bad acid trip. To go along with this show, you have to treat it as a happening and welcome the actors when they join you in your seat or, in my case, simulate sex in the aisle next to my feet. Led by Will Swenson as the top hippie, Berger, and Gavin Creel as Claude, they do all they can to make the happening happen.

But it is still a hard watch, even if you admire the courage of so many young Americans for briefly rejecting their parents' conformity. The hippies were right about Vietnam but wrong about free love and drugs. About female emancipation, they were Neanderthal. A bit of you waits for Berger to mature into Charles Manson. A newspaper critic wrote guilelessly at the time that Hair was full of moving parts. In fact, the nude scene is as static as a tableau from the Windmill Theatre. Yet when Claude lay dead on the American flag, the snow, unusually, falling over Vietnam, I was a little moved. We come to Hair to celebrate, but also to mourn a defeat.

Andrew Billen is a staff writer for the Times

Andrew Billen has worked as a celebrity interviewer for, successively, The Observer, the Evening Standard and, currently The Times. For his columns, he was awarded reviewer of the year in 2006 Press Gazette Magazine Awards.