The Icelander’s first major UK retrospective at the Barbican contains works to split your sides – and others to break your heart. Of the former, the highlights are his performance as a ludicrous Grim Reaper unmasked by a group of schoolkids and a video sequence of his mother repeatedly spitting at him. Of the latter, The Visitors is not only tragically beautiful but is also one of the finest works of art this century. It features Kjartansson and eight compatriots singing and playing his ex-wife’s emotion-soaked lament for their failed marriage . Each performer appears on a separate screen while we, the audience, stand or sit surrounded by nine different images that engulf us in gorgeous, hypnotic yet soul-searing music for 64 exquisite minutes. I was so overwhelmed I watched it twice – though a veil of my own tears. Astounding and unmissable.