Such rows are normal for public projects on this scale. Compared with the new British Library, which was savagely vilified for years as it was built (and turned out to be a great success, limited shelf space apart) Norman Foster's Great Court at the Library's former home, the British Museum, has had a relatively easy ride. Nobody with more than half a brain has challenged the quality or the logic of the design. It was fiendishly difficult to achieve, but the end result, like the original diagrams, has all the beauty of simplicity

You can, if you want, carp at some aspects of the work that Foster, de Grey and their team have carried out. You could argue that it is too perfect, too geometrical. The stone flanks of the "egg" are unrelieved, unmodelled, as smooth as - well, an eggshell. A grand commemorative carved inscription runs round the top of the re-skinned Reading Room, and that's about it. But don't be fooled: Foster is as classical an architect in his way as Smirke was before him. He's a man for symmetry, grandeur, the gobsmacking architectural effect. With Foster, what you see is what you get, and what you get is usually electrifyingly dramatic. Foster works not so much with stone or steel as with light.

For him, the relationship of the clouds outside with his new glass roof - the shadows chasing across the facade of the Reading Room, its interior now at last clearly visible from the court outside - is what makes it all worthwhile. For most of us, it will be the sudden revelation of the new. The journey takes you from the now re-landscaped, car-free entrance court (returned to something close to its original layout of raised beds and gravel walks), up the steps, through Smirke's imposing portico, and thence via the beautifully restored entrance lobby into the wide open space of the Great Court. It is a journey that begins in the light, takes you into the relative gloom of a Victorian cavern, and then suddenly releases you into the light again.

The point of arrival is the real test, because the Great Court project is meant to be all about the happy juxtaposition of the centuries, the restored and the brand new. Many old rooms previously stuffed with books are coming into service as new galleries. Soon the ethnographic collection, now nearing the end of its exile as the Museum of Mankind behind the royal Academy, will return here. And the restoration work is extensive. The high coffered ceiling of the entrance hall, for instance, is richly multi-coloured now. Before, it was painted out with plain grey emulsion. But underneath, researchers found traces of the original riotous colour scheme of 1847 by the designer Leonard Collman - his interpretation of how scholars then reckoned the insides of ancient Greek temples would have looked. Collman's original water-colours are in the museum's collection, so we can be pretty sure that this really was exactly how the BM once looked: the big early Victorian moment.

And then comes the big 21st century moment. You arrive in the Great Court, you look up, and you gasp. It is a very British thing. We don't stick a glass pyramid out in the open for everyone to see. We delay the moment of gratification. So, yes, the British Museum has done a Louvre. And from the outside, you'd hardly know. But once you're in there, you'll know all about it.