As a professional enigma, Beck Hansen has a reputation to maintain, and it is tiring work. He feels compelled to stay one step ahead of a demanding public. Already a master of pop collage - a niche art that recognises no boundaries between rock, hip hop or folk - he must be bored with being reliably unreliable. When he toured his recent Sea Change album around America with the Flaming Lips as his backing band, it was hard to miss the metaphorical sneer. If you think I'm off-the-wall, he seemed to snigger, check out these guys in their rabbit and dolphin costumes.

After that pinnacle of irony, there must have been nothing for it but to go the opposite way. For his first UK show in four years, it was just the man, an acoustic guitar and a couple of antiquated keyboard instruments. "My piano and my Wurlitzer," as he introduced the latter, acquired a special significance over the next two hours, because when Beck planted himself behind one or the other, he shook off the torpor that had settled in during the guitar numbers.

Essentially, Beck plus acoustic guitar plus wilted versions of folk-tinged Sea Change songs equalled twitchy audience (though they clapped, indulgently). On the other hand, Beck plus merrily burbling Wurlitzer plus playful takes on hits such as Loser and Where It's At made for ecstatic listening.

The unadorned guitar numbers brought out the teenaged stoner in this 32-year-old millionaire. But that is the risk you run when you lay a song bare: what you think is scalding honesty tends to sound like a fourth-former mumbling in a corner at a party. Yet when Beck unstrapped the guitar, restoring himself to goofball-savant status, all was well. As he jiggled through the kitsch Tropicalia on piano and got inventive with a turntable on Loser, the audience's delight spoke volumes.

It may not have been what Beck had wanted - my guess is he was seeking musicianly credibility by proving he could cut it with just a guitar - but in the end, it was the clever, tech-loving bohemian that roused the crowd. Isn't that always the way?

· At Usher Hall, Edinburgh (0131-228 1166), tomorrow, and the Ambassador, Dublin (0870 243 4455), Thursday and Friday.