Herbie Hancock, Barbican, London

There are many Herbie Hancocks: the master pianist whose subtle touch brought such colour and intelligence to the second great Miles Davis quintet; the composer, both of compelling grooves such as "Watermelon Man" and "Chameleon", and of more exploratory tunes such as "The Prisoner"; Herbie the vocoder-toting humourist; and Herbie the intellectual. You never quite know what you're going to get behind the presentational veneer.

His current band, with his old Blue Note compadre Bobby Hutcherson guesting on vibes, seemed likely to be thoughtful, perhaps revisiting the work that the pair did on the soundtrack to Bertrand Tavernier's Round Midnight. Too thoughtful, it turned out.

The warning signs were there on the programme notes. "What I don't want to do," said Hancock, "is make this a nostalgia tour. I'm interested in finding some way of constructing what we do that will be fresh and new to the audience." This took the form of a breaking down of one of Hancock's best-loved tunes, "Dolphin Dance", from the 1965 album Maiden Voyage. The 32-bar structure was taken apart, and each mini-section used as a basis for extended improvisation, resulting in a suite of epic proportions that took up the major part of the concert.

At the beginning, there was a gradual atmospheric build-up, Hancock, Scott Colley on bass and Terri Lyne Carrington on drums sketching a misty seascape, still waters barely visible until a chord from Hutcherson cleared the air and a semitone riff from Colley warned of rocks lurking near the surface. But without the occasional signpost to the audience, it was not clear to them that the captain of this ship had any definite idea of where he was going.

It was surely part of his idea of "playing in the moment" that such direction that there was would spring from the interaction of the quartet. However, this approach made little allowance for his listeners' desire to hear at least a vague exposition of the melody. When it came, it was in tiny fragments, and it was like going whale-watching. You wait such a long time that you're tremendously grateful for the briefest glimpse of a tail.

There were other problems. Hutcherson was (again) not miked up suitably for the Barbican Hall, and while the mid-to-low register came through clearly, the high notes struggled; you can only hit the vibes so hard. Lyne Carrington was too loud throughout, visible proof that it's not just boys but girls, too, who like giving a drum kit some welly. At times, I felt like striding on stage, wrenching the sticks from her hands and replacing them with a pair of brushes. Hancock himself was not audible enough, while Scott Colley, yet another bass player who inexplicably opts for woodiness over clarity, came over like a heavy weight wrapped in felt - it doesn't look sharp, but if you got in its way the impact would leave a dull, throbbing pain.

There were times when it did gel, when the quartet built something up and began to take off. But on one such occasion, at the end of a Hutcherson solo, I wondered whether the applause was as much for him as for the fact that the audience was treated to a phrase - all of six notes - from the melody of "Dolphin Dance".

There were, to be fair, other moments. Colley and Lyne Carrington locked together on a few grooves, on which she seemed more comfortable than swing. Towards the end, Hancock began to relax and show us just how fluent and fresh he is on an acoustic version of a Headhunters tune. But it was too late, for some restive listeners had already left the auditorium to fetch drinks, an action one would have deemed unthinkable beforehand, but understandable in the circumstances.

That said, Herbie Hancock is still a genius, and one of his concerts is always a worthwhile experience, however challenging or "out". He might have thrown the audience a few more bones, though.