Grant’s festival of everything from humour to electronic noise fed into his own heartbreakingly powerful headline act to make an unforgettable four-dayer for the City of Culture.

Subtitled “Sounds from Smoky Bay”, John Grant’s experimental festival brought together 47 acts from several countries in six venues over four days to celebrate the City of Culture’s Nordic links. However, the singer-songwriter’s involvement went far beyond creating the programme. He introduced acts, mingled with audience members and clambered up for an unscheduled bash at the piano. An enthralling, two-hour Q&A covered everything from his struggles with depression (“If you don’t commit suicide when you’re young, you develop coping strategies”) to tips for riding rollercoasters (“Get the car at the back for maximum whiplash”). Meanwhile, Hull was invaded by Grant lookalikes, complete with beards and Icelandic sweaters.

The festival was in his own image, too, reflecting the Reykjavik-dwelling American’s passion for the emotion and adventure of Icelandic and Scandinavian music. An eclectic bill stretched from subtle dance grooves (openers Tonik Ensemble) to contemporary jazz, via a Scandinavian Coldplay (atmospheric indie rockers Mt Wolf) to intense post-punk (Fufanu), although Hull electro-poets Cobby and Litten carried the local flag. Norwegian producer Lindstrøm turned City Hall into a space disco. Cabaret Voltaire founder Stephen Mallinder’s Wrangler delivered uncompromising electro-funk, while Icelanders GusGus satisfied the market for Erasure-ish electro-pop, fronted by an air-humping singer who formed his hands into a beak.

It was niche at times, but offered an education in bold, unusual music. There was throat singing (Leeds jazz mavericks Roller Bassoon), percussive sheet metal (all-female percussion trio Pinquins), while Nordic Affect’s piece de resistance was playing violin over the recorded gurgles of a breastfeeding baby.

Former Sugarcube Einar Örn’s ear-bashing electronic provocateurs Ghostigital came offering earplugs, ranted about governments and left to rapturous applause. Tadcaster poet Adelle Stripe’s Humber Star drew on her family history to tell a story of the devastating impact of death at sea, and the accompanying score by Halldór Smárason and Sinfonia UK really captured the cruel power of the waves.

In the stunningly lit Jubilee church, wine-sipping Norwegian singer Susanne Sundfør – an avant-garde Carole King – mixed breathtaking singing and entertaining farce. She admitted to being nervous and got her necklace caught in her guitar. “I’ve got a thumb pick,” she said at one point. “You put it on your … er …” “Thumb!” yelled the audience, to more riotous laughter, before Sundfør’s astonishing vocal range caused jaws to drop again.

Grant’s Sunday headline somehow fed all these disparate threads – from humour to emotion to electronic noise – into his own heartbreakingly powerful compositions, and a worldview formed by his sexuality, depression and religious upbringing produced a 90-minute gale of song. With his rich baritone backed by piano, synth and guitar (unusually, no drums), Marz and Where Dreams Go to Diesurely never sounded better. I Hate This Town became a giant clapalong. Grant mischievously but warmly dedicated GMF (“Greatest Motherfucker”) to “the people of Hull”, who responded with a rapturous ovation for a show – and a festival – the city is unlikely to forget.