Green Man Festival, Clyro, Powys The hills are alive with the sound of trembling knees

Power failures were as much a feature of this festival as they were of the Heath government. Again and again, a band would get going only for the generator to pack in and an uncomfortable silence ensue. During the performance of The Earlies, there was nearly more silence than songs. Of course, this being the Green Man, everyone accepted the black-outs with stoical good humour. Cruelly, you could say that given the state of some of the acts you needed a strong sense of humour just to be there. By apparently inviting back all the people who'd played last year, the organisers flirted with an obvious danger: would they be doing it for the art this time round, or for the beer?

Certainly, they wouldn't be doing it in a tent. Acts that one had felt indulgent towards in the Flower Show-like enclosure of last year's marquee, proved far less arresting on a proper outdoor stage, full moon or not. Now in its third year, the festival - nominally dedicated to new-wave folk but in practice a broad indie church - had doubled its capacity to a sold-out 2,000 plus staff and guests. Although still ridiculously small by the standards of most festivals, the increase in numbers tested the "infrastructure" (ha ha) of the Baskerville Hall site to the limit. Good weather and great music from the headliners made you forget most of the problems.

Will Oldham's Bonnie "Prince" Billy band was a revelation. If on record Oldham can seem too artfully artless, a post-grad gloss on Southern Gothic, in this context he's a knee-trembling rocker. With Matt Sweeney (formerly of Zwan) as one of three plank-spanking guitarists, they sounded as live and as dangerous as early Neil Young and Crazy Horse.

Joanna Newsom, who topped the bill on the closing Sunday night, was even better. The diminutive harpist-singer (tonight playing a Leviathan of an instrument at least twice her size) can, like Will Oldham, seem a little affected, what with that strangulated Betty Boop voice. But, once again, she's the real deal.

After an opening unaccompanied ditty delivered from the front of stage off-mic, she started what she said was a new song. As it unwound over a full 15 minutes or so, image following image as precisely as in a poem by HD, we were all drawn into her spell. Never mind the comparisons to Bjork or Kate Bush, Newsom is closer to the Divine Comedy, and I don't mean the dodgy band. I left the show renewed with love for the power of art, making resolutions to read Melville and Emily Dickinson. Put Joanna Newsom on the National Curriculum now.