Like a world within a world, Summerhall's Edinburgh Art Festival programme shoehorns into a single space a wide range of artistic visions and human experiences - though with corridors leading every which way, calling Summerhall a single space is like calling Mervyn Peake's Gormenghast a bijou family residence.

Summerhall sprawls, then, and so does its art.

In the trashy, cacophonous day-glo splendour of Deluxx Fluxx Arcade, curator Paul Robertson has the festival's most beguiling installation: two basement rooms lined with kitsch posters, washed with ultraviolet light and crowded with pinball machines and old games consoles splattered with slogans like "Art is a lie". A third room displays grafitti-based abstract paintings executed in a joyful spraycan aesthetic. The whole thing is a collaboration between Brooklyn-based trio Patrick McNeill and Patrick Miller (who work together as Faile) and veteran street artist Bast. If you see nothing else, see this.

Susan Hiller presents Re/Sounding, which comprises a video piece and three rooms in which she responds to works by the artists Gertrude Stein, Marcel Duchamp and Joseph Beuys. Her interest in the paranormal and the subconscious is reflected in the video work, Resounding (Infrared) and in the Stein room, where she presents Normal Motor Automatism, 12 photos of crumpled pages from a book by the celebrated American Modernist. In the Duchamp room she shows four large C-prints, each a ghostly portrait of a different individual barely visible behind a blur of colours.

By far the most radical artist in the programme is ex-Throbbing Gristle lynchpin Genesis Breyer P-Orridge. For a decade and a half, he and his wife Lady Jaye Breyer (who died of cancer in 2007) made their own bodies their art as they began their so-called pandrogyny project, a series of (often painful) cosmetic operations designed to make them look alike. The idea was to create one single, fused identity. In a show titled Life As A Cheap Suitcase, the viewer is presented with art works - photographs, collage, sculpture - reflecting this journey and the philosophical reasoning which underpinned it. As well as offering an insight into two lives lived well beyond what's considered normal, it's also a story of a rather tender love affair. But with paintings made from semen, it's not for the faint-hearted.

Another memorial of sorts can be found in a retrospective of paintings by the late Caroline McNairn, mounted with the help of Andrew Brown, founder of Edinburgh's much-missed 369 Gallery. McNairn also died of cancer, in 2010 aged 55, and these large-scale works from the 1980s show what a loss she is to Scottish painting. Bold, bright, internationalist in subject matter but Scottish in character - they nod to everyone from SJ Peploe to Alan Davie - their appearance here is another feather in Summerhall's curatorial cap.

Below the big names and the surface sheen there are deeper currents. Move through the various exhibition spaces and certain themes begin to coalesce, most noticeably war and politics. It's there in the angry - make that furious - installation work of Peter Kennard and Cat Phillipps; in the disciplined but haunting drawings and watercolours of Britain's first war artist, Glaswegian Muirhead Bone; and in a showing of work by award-winning Palestinian photographer Mahmoud 'Ezz' al-Zanoon. His vivid images of life in Gaza are presented alongside extracts from the war diaries of fellow Gazan and blogger Rasha Abushaban, whose entries begin on July 9, as the first Israeli shells land, and end 20 days later as she runs out of fuel for the generator powering her laptop.

If it's two-fingers-to-The-Man agitprop you want, Kennard and Phillipps have created a War On War room constructed from scraps of burnt plywood and scrumpled-up newspapers, and decorated with images of world leaders stencilled on to the share price pages from the Financial Times. Obama, Cameron and Netanyahu all feature, their faces blurred but their likenesses still discernible. Pasted on a wall in the outside courtyard is the duo's brilliant and now-iconic Blair "selfie" - the former Prime Minister grinning demonically into his mobile phone as an Iraqi oil field burns behind him. If the Occupy movement had an art-jester wing, Kennard and Phillipps would be it.

Grotesque, dystopian, macabre and supernatural are all words that spring to mind in the installation Heart (Meteorite), the first UK showing for Swiss artist Augustin Rebetz. He has created the walk-through work in collaboration with compatriot Giona Bierens-de-Haan, and while on first impressions it looks like a cafe after a fight - a teetering confection of old chairs and salvaged plywood painted with arcane figures - on reflection it's more like an extravagant torture instrument from a steampunk novel.

Finally there's flightiness (with gravity) and humour (with teeth) in the work of Claude Closky and Tamsyn Challenger. Former street performer turned art provocateur Closky presents 10, 20, 30 And 40%, a series of airy, pared-down works on paper. It's a site-specific installation spread over four rooms, each devoted to one of those percentages. Most of the works show lines in biro or pencil, intercutting at (presumably) the relevant angle.

Challenger, meanwhile, presents Monoculture, spread across several basement rooms. The best is the one containing a series of historical instruments used for punishing people (usually women) such as the Scold's Bridle (or "brank") and the breaking wheel. These Challenger has painted in the familiar blue and white livery of FaceBook and given titles such as Selfie Brank. On a set of stocks, she has simply written "Like". The zeitgeisty feel of the work means it may not age well, but in the here and now its message is powerful.

Exhibitions at Summerhall, Edinburgh continue until September 26,