A 50^th birthday is a landmark occasion. One has plenty to look back on, whilst still having much to look forward to. Plus there’s all that life experience to draw on. What’s not to feel positive about? In the case of a gallery that’s built up a remarkable reputation as an innovative space for contemporary art outside London, sheer staying power is surely to be cheered and celebrated – "hear hear" for the next 50 years, and so forth.

A retrospective of an artist’s work is not usually a history of a working relationship, but in the case of Christo, this impressive exhibition of works from the past 40 years also marks two crucial partnerships: with his wife, Jeanne-Claude, who was his equal and co-creator from 1961, and with the Annely Juda gallery, which has mounted 12 exhibitions over four decades, as well as being intimately involved in their massive environmental “wrapped” pieces. Photographs of the end results are breathtaking, but even more gripping is watching the development of the processes over the years.

Hard on the heels of the death of Lucian Freud comes the departure of another British art great, an artist who was Freud’s exact contemporary but who seems to belong in a different aesthetic universe – Richard Hamilton. While he was the more influential of the two, by some distance, Hamilton was never a contender for that nonsensical soubriquet "Britain’s greatest living artist". His work was too challenging, too difficult to pin down and it never told Britain anything it wanted to hear about itself.

After three days' motoring and clambering around the most awesome natural landscapes I've ever seen, how could a mere concert hall in a city the size of Cambridge begin to compare?

For her latest project, A Living Man Declared Dead and Other Chapters I-XVIII, American photographer Taryn Simon spent four years searching out families the world over whose lives have been defined by circumstances largely beyond their control – not natural calamities like floods, fires or earthquakes, but events orchestrated by other people. The stories are extraordinary.

It is now 37 days since Ai Weiwei was detained at Beijing international airport by the Chinese authorities. His family and friends have heard nothing since. His lawyer, to whom under Chinese law he must have access, was arrested as well, and since his own release he too has heard nothing. Officially, unless charges are brought today, the period in which he can be held without charge expires. And yet, where is Ai Weiwei? The whereabouts of Ai Weiwei the man are unknown. In London, however, Ai Weiwei the artist makes two stellar appearances.

Louise Bourgeois died last year at nearly 100, a revered figure: survivor of the Surrealist movement into the 21st century, a pioneer of autobiographical expression, whose fame came only late in life. Tracey Emin, by contrast, found fame early, coming to the attention of the general public in Charles Saatchi’s Sensation show at the Royal Academy while she was still in her thirties.

It is probably a worrying sign when the computer games of your youth become the historical butt of a conceptual art joke. Digital artist Cory Arcangel, who appropriates video-game technology, repurposes and redesigns it, has installed 14 10-pin bowling computer games in the Barbican's Curve gallery, and if you remember the earliest, an Atari, you're almost certainly as obsolescent as it is.

Who could not love Martin Creed? The tweed-encased harumphers of the world adore him, because they can say, “That’s not art,” and, “My cat could do that,” and have an all-round wonderful time. Conceptualists have it easy: what could be more fun than his Turner Prize-winning Work No 227, a light going on and off in a room? And lovers of abstract art love him because his work is just there. “Take it or leave it,” it seems to say. And they love him because, well, because his work is lovable.

Gabriel Orozco has been something of an art-world secret, for some mysterious reason. He has been fêted at the Venice Biennale, he showed at the prestigious Documenta in Kassel, had a blazing Serpentine show, an Artangel commission and been flavour of the month for more than a decade to those who follow contemporary art. But to the general public? Nada, nothing, zip. And God knows why, for, as this fine Tate retrospective shows, Gabriel Orozco is the real McCoy; a dazzling creator, a serious thinker, a joyous, liberating mind and a pair of eyes that helps us see new. On top of that, as an artist he has charm to burn. For heaven’s sake, what’s not to like?

Gabriel Orozco has been something of an art-world secret, for some mysterious reason. He has been fêted at the Venice Biennale, he showed at the prestigious Documenta in Kassel, had a blazing Serpentine show, an Artangel commission and been flavour of the month for more than a decade to those who follow contemporary art. But to the general public? Nada, nothing, zip. And God knows why, for, as this fine Tate retrospective shows, Gabriel Orozco is the real McCoy; a dazzling creator, a serious thinker, a joyous, liberating mind and a pair of eyes that helps us see new. On top of that, as an artist he has charm to burn. For heaven’s sake, what’s not to like?