Andy Warhol: 50 years on the pop icon still shines When I visited New York in my twenties, the Museum of Modern Art was my first port of call. Now, I can hardly wait to get to the Metropolitan, the kind of museum you want to live in. It's not just that you can get lost on the way to the loo and find yourself surrounded by French porcelain and fans of turquoise and gold - next to a rare chunk from a medieval arch. It's that after extensive and ongoing renovation, the museum is one of the most beautiful in the world. The range of gorgeous objects on show is almost enough to make you forget this is an art gallery that has one of the great painting collections. In the Post-Impressionists section, you can walk down an entire wall of Van Goghs with no crowds blocking your view. There is a wonderful early Andy Warhol there too - Ethel Scull 36 Times, from 1963 - and those Warhols in the Met's collection have now been joined by a new exhibition: Regarding Warhol: Sixty Artists, Fifty Years. This, the museum claims, is the first show to explore Warhol's influence on contemporary art. It is also one of the biggest contemporary shows that the Met has mounted. Its irrefutable argument is that if an artist's significance is judged by the possibilities he opens up for others, then Warhol is one of the most important of the past half century. Things he pioneered - merging photography and painting, turning film into art, examining society through the prism of its commerce - are now artistic currency. Sometimes it tries a little too hard to make its point: I am not sure how much Alex Katz owes to Warhol, particularly since Katz claimed that his blond-haired contemporary had stolen both the idea and the subject of his portrait of Lita Hornick. In the same way, Gerhard Richter, born just four years after Warhol, in 1932, may paint portraits that are based on photographs but there the resemblance ends. Nor is it clear to me that Ai Weiwei's potent Neolithic Vase 5000-3000BC owes any more to Warhol than it does to Marcel Duchamp. Whatever its origins, it is as swift and brutal an indictment of cultural consumerism as you are ever likely to see. The best of Warhol's successors in this show are those who take his lessons and rewrite them for their own purposes: Hans Haacke's Helmsboro Country, for example, a fierce plea for freedom of speech in the form of a giant sculpture of an adapted Marlboro packet; or Cindy Sherman's and Matthew Barney's reimagining of American myths; or Richard Artschwager's Rockefeller Centre. None of these pieces looks sub-Warholian, but all owe him a debt. The main result of this show is to make you realise what an extraordinarily good artist Warhol himself was, especially in the early days, when his work had a rough-hewn power that captures both the shiny surface and unsettling depths of American life. But a secondary effect was to make me regret his influence on some who came after: Jeff Koons may be popular but the crassness of his gold statue of Michael Jackson and Bubbles is as empty as the culture it seeks to expose. On the other hand, Tom Sachs's 1996 fashioning of a chainsaw from Chanel leather at first seems superficial, but is an image that lingers and troubles. That, in the end, is the most interesting revelation of this engrossing exhibition. When people say they don't like contemporary art, they are lumping together things that must be separated. In these rooms there is some very good work: and some that struggles to stand the test of time and judgment. It is deciding which is which that is so fascinating.