I love Green Man. The smallish festival is the second most beautiful site I’ve ever visited (after G Fest, which is situated on a beach in a fjord in the Faroe Islands). Nestled in a valley between the mountains of the Brecon Beacons, it has great bills, it’s impeccably organised and I feel nourished by it. But, in the interests of being honest about festivals for those who have never been, I should also confess that this year it supplied the single most miserable experience of my music-watching life.

Friday was the kind of day Noah might have felt a little discombobulated by. It began raining before dawn and it never let up. Come nightfall, the wind picked up too. During The Comet Is Coming – the fêted trio that bonds the alto sax of jazz star Shabaka Hutchings to the tempos and analogue synths of classic rave – the combination of the wall of sound and light with the horizontal rain was thrilling in a here-comes-Armageddon sort of way. Come the headliners, Devo – the American art-rock group now on their farewell tour – I was desperate to get something warm inside me and walked up the slope to one of the food stalls. In the dark and wind and rain, and in mud that would have done credit to the Somme, I slipped and twisted a knee. It was midnight, in a field in Wales, and I was lying face down in six inches of mud, clutching my leg, yelping. This is not what being a music critic is meant to be.

That rather overshadowed Devo for me, which was a shame because they were terrific. They’re one of those bands who are often misunderstood as a novelty act, but at Green Man they played a fantastic set of skew-whiff rock ‘n’ roll. Their famed cover of ‘(I Can’t Get No) Satisfaction’ was the dreariest moment, not a patch on their own ‘Girl U Want’ or ‘Uncontrollable Urge’. Given the weather, the crowd was sparse, but every single person there seemed wholly committed.

On the Thursday, accompanied by strobes that could have triggered every epileptic in a 30-mile radius, Spiritualized were overwhelming. Meanwhile, Self Esteem, whom I reviewed in these pages at the start of her album campaign two years ago, has become an authentic pop star in the intervening period, full of vim. Her status at the top of the bill – something I doubted was possible when I first saw her – was entirely justified.

There were big treats, as ever, down the bill and on the secondary stages. I left Self Esteem early to see the end of the set by the typographically challenging LA hip-hop trio, clipping. (the full stop is part of their name). It was claustrophobic and intoxicating. The accompaniment was not samples of funk and soul, but sheets of electronic noise, and Daveed Diggs’s lyrics were bleakly complementary. ‘That’s when the Jaguar emblem/ Crashed through the driver-side window/ And the driver of the Jaguar’s head left his body/ Still sitting in the rental/ The couple all bloody/ Tongues punctured by each other’s teeth,’ he raps on the closing song, ‘Story’.

In the drizzle of Friday afternoon, the Welsh band Melin Melyn were a fizzy delight, their set presented as a conceptual piece about a not-very-good supermarket. They’re firmly in the tradition of Welsh psychedelic whimsy, following in the footsteps of Super Furry Animals and Gorky’s Zygotic Mynci – groups with absolutely no shame about making their tunes sound like nursery rhymes or letting their imaginations take them to places pop rarely goes. (They also did an unexpected cover of ELO’s ‘Mr Blue Sky’, which, for no reason I could identify, made me cry.) I felt rather sorry for James Ellis Ford, who followed them and played a wonderful set to a quarter of their crowd.

The single most exciting thing, though, was the appearance of the reunited New York garage rock band The Walkmen. Yes, they obviously love the Velvet Underground and Bob Dylan, but they have their own voice, and their singer Hamilton Leithauser had more charisma than the rest of the bill put together. The Walkmen pull off the rare trick of being hugely accessible without being obvious. The songs never quite do what you expect: they stay quiet, or they explode in the wrong places. They are the most underrated rock band of our times, and they play three London shows next week. Go.