Damien Rice, Shepherd's Bush Empire, London

Midway through his London show, it all goes horribly wrong for the Irish singer-songwriter Damien Rice. The effects pedals appear to be misbehaving, and there's no sound coming from the speakers. Clearly exasperated ("We should have named this the Technological Nightmare tour," he grumbles), he steps forward and sings an unplugged version of "Cannonball". It's the best song of the evening, one that, stripped of effects, conveys a warmth and humanity that has been conspicuously absent all night.

There are, of course, plenty of arguments against Rice's mere existence. Right now, music needs another meek, acoustic-guitar-wielding troubadour like it needs another Phil Collins. There are, too, the inevitable comparisons with that king of coffee-table acoustic rock David Gray, with whom Rice shares both management and record company. For many, Rice's O is the new White Ladder, a breakthrough album stuffed with soulful ballads that artfully pluck the heartstrings. Also like Gray, Rice is wilfully unglamorous and about as charismatic as cold porridge. And are my eyes deceiving me, or do I detect a little twitch when he reaches for the high notes?

Rice is, it seems, acutely aware of the pitfalls of being a confessional singer-songwriter and to prove it sings "Childish", a rather bitchy little ditty that sends up the worthier-than-thou songwriting style of the so-called New Acoustic Movement ("I'm a dandy little dreamer/ I'm a doctored misdemeanour/ A didactic destiny-schemer/ Bear with me, will you?"). It's a bit rich, given his own penchant for introspective lyrics and guitar-led histrionics.

Tonight's set draws heavily onO, though the songs are given added vigour with grainy guitars and some ferocious drumming. Another of Rice's favourite tricks is to feed his voice through an effects machine, making him sound as if he's singing through a megaphone. It may work wonders forPJ Harvey, but for Rice it sounds more Hyde Park Corner on a damp Sunday afternoon. His attempts to beef up his songs simply underline the fact that they're feeble facsimiles of better ones by Radiohead, Coldplay and, yes, even David Gray. While he has an ear for a memorable melody, his lyrics (sample: "I can't take my eyes off you") are often overwrought and sentimental.

Near the end of the show, our host vacates the stage in favour of the cellist Vyvienne Long. Her version of "Seven Nation Army" by The White Stripes deservedly gets the biggest cheer of the evening. It doesn't do Rice any favours, though, drawing our attention to exactly what has been missing in his set, namely, humour and heart.