The Watts Gallery in rural Surrey is a very genteel setting for a show by a figure who for most of his life was denied polite society. Richard Dadd spent 42 years in mental hospitals, first at Bethlem, then Broadmoor.  As one can infer, he was criminally insane, and despite a disarming interest in fairies, his life and work cannot be spun into a happy-ever-after narrative.

One of the earliest surviving sculptures by Barbara Hepworth is a toad made from a khaki-coloured, translucent stone; you can imagine it cool and heavy in your hand, not so very different from the animal itself, in fact. Made nearly 30 years later, the monumental sculptures carved from African guarea wood are almost unbearably touchable, each one with its dark, glossy exterior cracked open to reveal an inside as creamy as a conker. But while we are denied the pleasure of touching these objects, looking at Hepworth’s work is in itself a gloriously tactile experience.

The hook for Alan Yentob's portrait of the 86-year-old architect Frank Gehry was the initiation and progress of an enormous new building in a rough portside area of Sydney, the Dr Chau Chak Wing Building for the business school of the University of Technology. It opened after nearly two years of construction, on time and on budget, last autumn. To commission it, the dean of the school, Ron Green, simply rang Gehry up, and Gehry replied with just four words: "I’m up for it." 

Light. Light banishes the shadows where monsters lurk and where ghosts rattle their chains. “Give me some light, away!” cries the usurping king in Hamlet as his murderous deed is exposed by the trickery of art. What guilt plagues and seizes his conscience, and yet Claudius, conflicted, cannot pray. He must, therefore, remain a captive among the ghosts and the monsters where no light may fall.

If they remember the 1960s at all, the ageing population of Bexhill-on-Sea will remember Bridget Riley for her black and white experiments in perception. The iconic results of this line of enquiry can still result in a “happening” for the eyeballs. And that’s exactly what you get from the earliest paintings in this show: uniform stripes of black and white that won’t for a moment stay still. 

For all the wrong reasons, the work of Dexter Dalwood serves as a useful metaphor for this exhibition. Trite, tokenistic and desperate to look clever, Dalwood’s paintings are as tiresomely inward-looking as the show itself, which is a dismal example of curatorial self-indulgence at the expense of public engagement.

A steel corridor stretches as far into the distance as you can see (pictured below right); the gleaming sides and gently sloping floor invite you to step inside but, as you venture further in, it gets darker and darker until you are groping your way in pitch blackness. This unnerving experience reminded me of when, as a child, I followed my parents deep into the cliffs of north Cornwall as they gingerly crept along disused mine shafts, lighting the way with matches that quickly fizzled out.

Enzo Green, Shirim, Raethro Red, Raemar Magenta. Everything has a name. But beyond the meaningless but musical sounds of their titles, the light projections and installations on view at Houghton Hall by the leading American light, land and skyscape artist James Turrell are an ineffable art whose presence and effect is subtle, substantial, utterly memorable and almost beyond words.  

It's impossible to overstate the reverence accorded the painter Agnes Martin by her fellow artists; in the panoply of American cultural goddesses, she is right up there with Emily Dickinson. Yet she is scarcely known in the wider world, partly because her work is relentlessly abstract, but also because she was deliberately evasive.

Imagine if broadcasters thought the only living pop star worth giving air time to was Lady Gaga. Imagine – the horror. It would be wall-to-wall Gaga for the foreseeable future. And then imagine if the only living contemporary artist commissioning editors at Channel 4 and the BBC even bothered looking at was… Grayson Perry. Imagine.