If you’ve seen pictures of the Ballets Russes, then you’ve seen Hoppé photographs. But then, if you’ve seen any society pictures from the 1920s and 1930s, then you’ve seen Hoppé. And famous writers. In fact, for portrait photography in Britain between the World Wars, you can pretty well bet the photo is Hoppé’s. But what's so good about this new exhibition is that it shows a side to Hoppé that is much less well-known - the street-view. And these photographs are thrilling, in form as well as content.

Jan, or Janin? Gossart, or Gossaert? Or Mabuse? After a mere five centuries, we haven’t settled on a name quite yet (even for this exhibition: at the Metropolitan Museum, the same show spelt it “Gossart”). We don’t know where he was born, although Maubeuge, then in Hainault, now in France, is the best guess, hence “Mabuse”. His birth date too is a mystery: the Grove Dictionary of Art suggests 1478, while the National Gallery just shrugs and gives us “active 1503”. What is in no doubt, however, in this very model of an exhibition, is that Jan Gossaert represented not merely one of the peaks of northern Renaissance art, but that, in a constantly surprising career, he also synthesised great swathes of the Italian art world, both classical and Renaissance, creating something new and hugely potent.

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.

Does watercolour painting suffer from an image problem? Do you think of the wild, vaporous seascapes of Turner, or Victorian ladies at their sketchbooks dabbing daintily at wishy-washy flower paintings? Do you associate the medium with radical innovation or with staid tradition? And would Jackson Pollock have appeared quite so heroic flinging thin washes of watercolour around instead of viscous oils?

After writing about a recent survey of French artist Philippe Parreno at the Serpentine Gallery last year, I found myself wondering about his collaboration with the Scottish artist Douglas Gordon. In 2006 the two artists made the acclaimed film Zidane: A 21st Century Portrait, and while Parreno’s skills as a film-maker were pretty evident from that first UK solo exhibition, Gordon’s talents must surely lie elsewhere - that is, outside the frame. Neither technically ambitious nor visually seductive, his films are not even meant to be seen in their entirety, certainly not his 1993 24-hour Psycho, which is simply a frame-by-frame re-presentation of the Hitchcock classic.

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.

Susan Hiller describes herself as a curator as well as an artist. She makes work out of objects that she’s collected over the years. She collates information, too, and personal testimonies. These all go toward making works whose primary aim is to question meanings and categories and belief systems. These belief systems are those that are often found on the outer fringes of mainstream norms – or, if you’re put off by the dry language of academe – which Hiller isn’t – the loopy stuff that’s a bit “out there”. Paranormal activity, alien abductions, séances, the healing power of holy water, levitation, auras. All these are dealt with in Hiller’s work.

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.

Austere, elegant, impressive. Edwin Lutyens’s Whitehall Cenotaph is a thing of beauty, a monument that embodies permanence in the face of all that is impermanent, and solidity in the face of all that is ephemeral. It’s an inspired decision to bring it indoors, for inside a hushed gallery, away from the rush of traffic and stripped of its flags and sculpted wreathes, Lutyens’s memorial can at last be properly admired as a work of art.

The first thing to make clear is that Robert Mapplethorpe, notorious for his photograph of himself with a bullwhip up his arse, is not really a photographer: he is a sculptor who works in the medium of photography. What else can explain the marble and ebony of his chiselled subjects, or the fact that most of the works selected for this show as responses to Mapplethorpe are sculptures?