It's like encountering a long-lost, legendary uncle, away a long time at the wars. At first there is almost a stab of disappointment, as the mythic stranger turns out to be just human-scaled after all. But then, as you look at the slight smile, the long elegant fingers, and get the unique measure of him, the old fixed image gives way to something richer, warmer, funnier than you ever expected. What was revered, marvelled at, becomes intimate and human and ... lovable.  In the old pictures, he was just a face in a regimented rank of grey warriors. Now he stands separate and close to you: an infantryman, a charioteer, a general, an archer and - it is impossible not to feel as you look into those gentle eyes - a father, a son, a husband.  So, here they are, and this is it. I am looking into the eyes of one of the terracotta warriors from the tomb complex of China's First Emperor, a part of the most famous archaeological discovery of recent times. Since it was found by chance in 1974, it has inspired artists, even changed art, echoing in the work of Juan Muñoz or Antony Gormley even as it dazzles in magazines and on TV. The British Museum has just put the final touches to its exhibition that boasts the biggest loan of these life-scaled, meticulously detailed, painstakingly differentiated figures ever to leave China. They stand now beneath the great blue dome of the old British Library reading room, and somewhere beneath the exhibition's temporary staging is the desk where Karl Marx wrote Das Kapital, which in the light of Chinese history surely adds a layer of meaning. But does this year's most anticipated exhibition live up to the images of those ranks of terracotta soldiers we are familiar with? What are you actually going to see?  You're going to see, it has to be said, quite a lot of films, slides, gigantic photographs and modern models before you get to the warriors. These multimedia teaching aids, along with lucid displays of bronze and jade wares and weapons, tell what seems to me to be a strangely simplified version of Chinese history, with a rhetorical spin that might be mistaken for a glorification of the authoritarian state. I don't want to get into arguments about Chinese history but ... here goes.  It's fair enough to call the exhibition "The First Emperor", which is indeed what the king of Qin called himself after conquering all of China in the late third century BC. King Zhen of Qin was the first to unify All-Under-Heaven, as it was known, and the first builder of the Great Wall. He gave China common weights and measures, and currency. Yet he was to be remembered as a monster: the ancient Chinese historian Sima Qian, writing a century after his reign, saw him as a tyrant who massacred prisoners, burned books and slaughtered scholars.  There is no archaeological evidence to back up Sima Qian's worst accusations. On the other hand, he did live a lot closer in time to the First Emperor than we do, and the determination today to reject his view is a bit intemperate. Why can't a man who has a wonderful tomb also be a monster? Hitler planned a great mausoleum, too. This exhibition, which celebrates the First Emperor pretty unreservedly, might be accused of whitewashing an authoritarian ruler, but perhaps more misleading is the fact you can leave without realising that Chinese civilisation predates the First Emperor: it gives the impression there was nothing much before him, and continuity after him. Neither impression is correct. Great Chinese thinkers, not least Confucius, flourished 300 years before the conquests of Qin. Nor was there continuity from Qin to the fall of Imperial China in 1911 - as if! The First Emperor's dynasty fell soon after his early death. And yet, none of these objections matter, because it turns out the First Emperor subverted his own memory, and turned his own cult on its head. This is an exhibition that ends up doing the opposite of what it claims. It turns into a poem of the people.  There is another problem with the multimedia dramatisations and big claims about the emperor's significance - they provoke suspicion. Is it all a distraction to stop us counting how many terracotta warriors have actually come to London? Because I only count 17. This is the biggest exhibition of these sculptures ever to leave China, but is it enough to vindicate the excitement? Yes, and a thousand times yes, there is enough here to wonder at, enough to change your view of art and make you think deeply about life - I just wish they had taken out insurance against people who count the raw number of figures and complain of hype.  Those people are wrong to be disappointed. The fact is that when farmers chanced on the First Emperor's underground army 33 years ago, they brought to light one of the most universal and beautiful works of art ever created. The tomb complex is a vast, single work of art we still don't know in its entirety, and what makes all my cavils irrelevant is how meticulously and intelligently this show does away with what you think you know about the terracotta army, and reveals it to be part of an even greater achievement that is so far only partly known. Some of the most exquisite figures here are musicians and acrobats discovered within the last 10 years. I want to say that again, it's so exciting: a pit of acrobats and wrestlers was excavated in 1999, and an underground arrangement of birds and musicians in 2000 to 2001. Both are crucial to understanding the world of the terracotta army.  A wrestler's vast torso spreads out in puffy clay that contrasts fantastically with the soldiers' disciplined bodies: you sense the craftsmen having fun here, layering on the clay to create this gargantuan mass of muscle. Beside him an acrobat holds a finger in the air, as if balancing some now lost object; nearby two musicians sit playing invisible instruments, while bronze swans and cranes listen attentively. This Orphic scene, like the acrobats, like the army, is lifesize. What it reveals is the true nature of the First Emperor's dream.  This was not simply a military man who chose to be buried with his army. According to Sima Qian, the First Emperor was fascinated by the idea of model worlds. Whenever he conquered a state, he had its palaces replicated, complete with women and entertainers: he created a kind of theme-park China, and brought the same vision to his tomb. At this time in ancient China, existence was believed to continue after death, and the tomb was a fully equipped base for the afterlife. Servants and courtiers joined you there, willingly and unwillingly. The First Emperor's tomb includes replica people and animals in terracotta, so he can rule an empire beyond death.  Originally all the Emperor's terracotta people were painted in vivid, lifelike colours: most of the pigment has gone from the soldiers, and when we picture them we think of ranks of grey figures. The recently discovered musicians, though, still have pigment on them. They still have pale faces and gently coloured garments. Yet what is so moving is how clearly they manifest the First Emperor's desire to live in a paradise after death. In the Song dynasty, more than a millennium later, China would produce the first great landscape paintings. It has been suggested the origins of those dreamy mountain vistas may be in myths of paradise, and the First Emperor's musicians play to birds in a pastoral idyll.  The First Emperor was making a paradisiacal palace-tomb whose full dimensions are not yet known. This exhibition reveals something incredible - that archaeologists have yet to dig into the actual tomb. In fact, the director of the museum of the terracotta army says there are no plans to do so. It is as if Howard Carter looked into Tutankhamun's tomb chamber, noted that it contained "wonderful things", and respectfully sealed it up again. Sima Qian claimed the tomb contained an image of the cosmos (recreated as a starry sky in one of this show's more distracting gimmicks), and a vast map of China's rivers and lakes made of flowing mercury. Tests have shown that the mound does contain high levels of mercury.  This wondrous underground realm needed guarding. Three pits full of terracotta warriors stood poised to protect the First Emperor from the vengeful ghost armies of his victims. And so they stand here, in London, in front of me - the most famous clay figures in the world. And the Emperor's plans subtly turn awry. Even in an exhibition called The First Emperor, which provocatively overturns thousands of years of Chinese vilification of a man remembered as a tyrant, he is not the star of his own show. These nameless soldiers are the stars.  Archaeologists insist none of the terracotta warriors is a "portrait". The creation of so many figures was a triumph of mass production: after assembling the figures from modules, they were given final individualising touches like facial hair. Yet I defy you to stand in front of them and not think of them as replicas of real people, as something more intimate and alive than a portrait, even. They are personages, beings, ghosts - they live.  In the western figurative sculpture tradition that began in Greece at the same time that Confucius was alive in China, and still flourished when the First Emperor's artisans created his tomb, movement and life are evoked through observation of muscle, proportion and action. The terracotta army is the final death blow to the long-enduring belief in the uniqueness and superiority of this Greek tradition because it achieves just as much life, animation and beauty, in a totally different and unrelated way. It is hard to describe the exquisite realism and simultaneous supernatural unreality of these sculptures. They move: they kneel, they crouch, and one looks as if he is performing martial arts, though in fact he was once holding a bow. More precisely, they have the power to move: they are silently awaiting orders. Their waiting has something exquisitely noble about it: the way they smile or look grave, the way they position their hands, the way they express strength in tranquillity.  There is a quality to these men that is absolutely disarming. They contain love. Whose love? You feel it comes from them, a warmth, a compassion. You get a sense not just of a slave army obedient to its ruler's command, but of real human beings with their own memories, commitments and responsibilities. Their loyalty to the emperor might be expressed, but also their duty to family, even to country. The love that endures in this art is above all the passion of the creator. What makes it a living art, despite lying in the cold grave so long, is that anonymous artisans, employed in the production system, put their own selves, their feelings, their love of life, into these sculptures. The terracotta army is not a tribute to power. It is a people's art - you might even say, the people's revenge.  Nor is it an entirely anonymous art. In the graves of convicted criminals who were forced to labour on the emperor's tomb, pottery shards record names like that of Yu, a low-ranking civil servant from Bochang. "Who built Thebes of the seven gates?" asked the Marxist dramatist Bertolt Brecht in a poem that wonders why the workers are forgotten and only history's great men are remembered. How he would have loved the terracotta army, and how he would have enjoyed this exhibition. How Marx's ghost might enjoy rising up from the desks below to savour it. Perhaps ancient historians exaggerated the crimes of the man who built the first Great Wall, but it's unquestionable that his achievements, like those of every great man, were based on the blood of the poor.  This exhibition does the opposite of what it promises, and is the better for that. It begins with "wonderful things" that Howard Carter would be greedy for, with cups of jade and jewellery of gold, and shining sword blades. Yet its true wonders consist of mere fired earth, the stuff of China's soil turned into masterpieces of realist art. What survives of the First Emperor? Nothing but what his people gave him; nothing but the passion of the artisan who cared enough to put every little ribbon on that suit of armour. The emperor is gone. The human endures.  The First Emperor: China's Terracotta Army is at the British Museum, London, from September 13 until April 6 2008. Details: 020-7323 8181.
The First Emperor's invasion of the British Museum is the most anticipated exhibition in years. Jonathan Jones gets the first look and is rewarded with a fresh perspective on an old foe.