Calatrava's architectural reputation has been transformed. In commercial terms he was massive anyway, with a new opera house in Tenerife and a big extension to the Milwaukee Art Museum among the recent additions to his portfolio. His stadium and sports complex for the Olympics in Athens this summer are under way. At 52 he is five years younger than Libeskind and has built exponentially more. A rare, possibly unique example of a combined architect, engineer and sculptor, he started his prodigious career in the early 1980s with a station in Zurich, came to the world's attention at the Barcelona Olympics of 1984 with the first of a long and continuing sequence of flamboyantly beautiful bridges, and quickly found himself with the complimentary First Class champagne as one of the world's elite handful of globetrotting "signature" architects.

But it looked as if success had gone to his head. He is a trophy architect, hunted by the world's great cities for his signature bridges. There is no doubt that he pushes engineering in ways it does not always want to go, usually making his structures over-elaborate. Some of his buildings started to go way over the top. Projects such as airport buildings in the form of abstract birds were acclaimed - the imagery seemed right - but he marched on into ever more overtly expressive projects. His "City of Arts and Sciences" in his native Valencia includes a planetarium in the form of a huge human eye. The Tenerife Opera House has a frankly alarming canopy in the form of a giant concrete breaking wave (or protruding tongue, if you prefer). At Milwaukee, he explored several of the ideas he has now revisited at Ground Zero, but again it is more than a little overwrought. A building with slowly flapping wings, which alternatively looks like the tail-fluke of a diving whale? What's that all about?

So Calatrava's academic mien is misleading. He is a rampant exhibitionist. He needs to calm down a little. No, make that a lot. Given which, it is strange that it should be the hothouse atmosphere of New York that has done him most good. The new station certainly has the wow factor, but for Calatrava it is positively restrained. You can see that he has worked and worked at it, thinking about the context, thinking about getting light right down to the underground platforms, thinking about how it will look from above, how it will provide a gathering-place in the park, thinking about how best to capture Libeskind's cherished "wedge of light" as falls across the site on September 11 every year: indeed, sliding open the roof hydraulically to welcome and celebrate it. The angle of the wings of the building are set out from the two positions of the sun that day between the time of first impact and final collapse, an hour and thee quarters later.