John Maus. A man jumping on the spot surrounded by flashing lights, screaming over echoed samples of his songs in the "Klubben" tent. Not everyone's cuppa tea, sure, but this picture of straining anguish is a more successful one, it might be argued, than even Edvard Munch's, The Scream, which pulls people from around the globe to Oslo. The Minnesotan's defiant, clenched fists tug violently on his trousers and shirt. He punches himself in the face. It's at odds with the twinkling, spritely music and gives an answer to hypnagogic/hauntological associations as if he might as well be screaming CALL THIS FUCKING CHILLWAVE?!

It's quite apt that this gig takes place inside the medieval park where Øya Festival is held each year. Last year's critical smash We Must Become The Pitiless Censors Of Ourselves – the album that he sings most songs from here – is influenced by medieval chants and religious music as much as 80s synthpop. It feels like a knockout, standout performance precisely because it resists performative expectations, remaking Maus in front of our very eyes as not someone who merely apes the record that has bought him to people's attention. The key song here is Maus' ode to a creative life free of other people's power-games, his cover of Body Count's ‘Cop Killer'. In a way, he's standing up against a tidal wave of inconsequentiality that threatens to engulf music in the 21st Century. You can feel it coming on at times at Øya 2012. What is it all for, he seems to be demanding to know, if you are just going to turn up, play your songs, and leave?

I know the fans are ultimately paying for the Stone Roses' reunion, but watching the band flog this reanimated horse over at the main "Sjøsiden" stage on Wednesday, the first night, you wish they would hold a collective meeting and stop making this seem so saleable, so appealing for promoters. The out-of-tune vocal and limp rhythms without the mass euphoria of Heaton Park to back it up is pretty unbearable so it's off to see Susanne Sundfør, from Haugesund on the west side of Norway, but currently residing in Oslo. Sundfør's pixieish, quivering vocal floats over clever synths, heavy bass and solid beat. Its subtle, creeping power takes hold until it seems to nail the beauty of her country, the thumping knockout that much of Norway possesses. The crowd grows as crystal-clear synths twinkle in the dusk.

The hyped-up Anglo-Francais quartet, Savages start Thursday off with a thwack. Lead singer Jehnny Beth rocks from side-to-side, agitated and amphetaminally. Ayse Hassan plays her low-slung bass so naturally it's as if it's part of her. Drums pound the chests of audience members. It's a good set, much better than the slightly anti-climactic gig at the Shacklewell Arms in Dalston, most noted in the press for the names of audience members (indie label kingpins Daniel Miller, Geoff Travis, Jeff Barrett and Martin Mills were there) than the gig itself. The PA here (Øya uniformly has excellent sound) and the space sets the music free. The surely intentionally Patti Smith-esque ‘Husbands' and ‘Shut Up' are highlights. It's brutal and stark, wiry yet beefy. Is it the tail end of the last post-punk revival or the start of a new one? Perhaps it's neither. With the solid-as-steel back line and out-of-fashion reference points they might potentially be this generation's Dr Feelgood. During this lightning-quick year, the band has acquired a kind of assurance and snarl that once emanated from Canvey Island's razor-sharp bluesmen.

Despite (or perhaps because of) his status as the man of the summer thanks to the success of Channel Orange, Frank Ocean doesn't seem all there when he arrives on stage. Flanked by two guitarists, he stands in front of a Baudrillardian backdrop of a United States flag made up of television sets that depict various clichés of paradise. "You all look beautiful," Ocean says obligatorily in monotonone. He sings ‘Summer Remains', a lesser-known song. "Not even the palm trees can save us from the flames" he intones, ominously. Minutes later he leaves the stage. An announcer comes out to say Ocean has lost his voice.

St Vincent, aka Annie Clarke, seems to have stolen the energy that Ocean was missing. A composer of whimsical, magical songs about transcendence of ordinariness, Clarke is a descendant of Hendrix and Dolly Parton, Laura Nyro and David Byrne (who she is releasing an album with later this year). The set gusts along with the force of last year's brilliant Strange Mercy, but live the Texan is an even more exciting prospect than on record - her guitar playing fizzes on ‘Cruel', and she wins extra points for liberal use of theramin.

During Billy Bragg's set it is difficult to know if the Norwegians are completely following the long digressions between songs. This is a country that ensures that a high percentage of its citizens can speak English, but, as Bragg acknowledges, they might not have learned how to understand Barking Estuary. He has beef with Twitter bullies: "Freedom of speech does not give you the freedom to abuse people." And there are cheers as he evokes Woody Guthrie while meandering towards the elephant in the city – the bomb and gun attacks on Oslo and the island of Utoya to the north, which happened barely a year ago and unfortunately made Anders Breivik the most famous living Norwegian. It could have been cringe-making, but it's handled with his consummate directness and sensitivity.

It sets up the rest of the day as a kind of preaching session. A$AP Rocky's at it – with last year's globally broadcast events still at the forefront he declared, "It don't matter if you're black, brown or yellow – we're all purple people!" And what is headliner Bjork's iPad app/album project Biophilia but a mad, glorious lecture on the wonder of nature and the importance of understanding and respecting it for the future of the planet. Bjork, clad in a sparkly dress with a design on the front that can only be described as intestinal, is backed by big bad drums and an incredible female choir who throw themselves around the stage while achieving pitch perfect, complex harmonies. After a few visits of the newest, seemingly permanent addition to the World of Bjork, a tesla coil, she and her choir run through a few old favourites, ‘Possibly Maybe' and ‘Declare Independence'.

On Friday afternoon, Metronomy play a set largely taken from last year's summery belter, The English Riviera, a record full of smooth beats and bright hooks that translate well here as the sun beats down. The thing about Metronomy is, for all the funk of the record it never quite feels completely smooth – you can still feel elements of self-consciousness, which is not to declare a negativity. It's what gives the record its odd pop power, buzzing, as it does, between aspiration and fulfilment, the desire to make music as pure as white sand but with the reality of awkward Englishness following close behind you.

In the tent, Dam Funk has no such issues, which I suppose is the point. No use comparing. This is sex, sometimes down and dirty, sometimes cloaked in velvet romance. "Someone loves you! Someone loves you," cries Passadena's Damon G Riddick as some start to file out for Odd Future, which, compared to this Stevie Wonderist brilliance, is like leaving a warm, loving bed to go and watch Jackass on your own in the spare room. Compare the two approaches to love and relationships thus: "It's such a pleasure to know you... I will always treat you right," Riddick intones on ‘I Wanna Thank You (For Steppin Into My Life)' Outside on the main stage, OF put it somewhat differently: "MY BITCH SUCKED DICK LIKE SHE SUCKED DICK!"

After a taster of Chromatics' detached disco it's time for the Congos, the legendary, harmonising reggae band whose 1977 LP Heart Of The Congos is regarded as one of roots reggae's finest. They light up the festival. The backing band are punchy and set people dancing (which is a feat as Øya isn't much of a dancing place). Soon Max Romeo comes on, leading a chorus of "I'm gonna put on an iron shirt / And chase the devil out of Eart'", followed by the introduction of junior dancehall duo, Romidal, and the increasingly-befuddled Heart Of The Congos producer, Lee Scratch Perry. But the three Congos, are the stars tonight; the Jamaicans' energised rendition of ‘Children Crying' might be the single high point of the four days. It might sound patronising to register surprise at how supple the trio are, how loose and elastic their dancing is on stage, but it's quite something to see.

The death-rattle growl of Haugesund's Årabrot greets us on Saturday. Topless in denim shorts; pasty skin vs beating sun, provoking a fair amount of headbangs down the front with the white-light gravel of Kjetil Nernes' vocals and scab-scratching guitar.

After the small-time-soul-singer-made-good, Charles Bradley, tells he loves us over and over to a pleasant soul groove, it's time for SBTRKT's mix of smooth vocals and brockout drums. Walking back to the hotel via the half-built developments that will apparently provide homes and offices to tens of thousands of people, the music floats, quivers, booms across this side of the city. Bass and treble war with one another between the cavity of a future high-rise building and the side of a freshly-erected one. The wob-wob throb of immortal track ‘Wildfire' scatters off the side of the newbuild, and the sample of Little Dragon's singer Yukimi Nagano's vocal achieves a Burial-like quality. Despite the fact that its main sponsor is a bank, Øya still feels like it belongs to Oslo – locals can enjoy the music without a ticket if they hang out on the bridge that overlooks the festival, such is the quality and volume of the sound. It will be interesting to see if such volume will be achieved once these high-rises are full of people.