Build a flashy new culture palace in any middle-ranking city these days, and the words "Guggenheim effect" are sure to turn up faster than the tourists do. But with Valencia's new opera house, the Palau de les Arts Reina Sofía, perhaps we should be talking about a Gaudí effect. It's a flashy new culture palace all right, designed by one of the world's premier league "starchitects", Santiago Calatrava, and it could well do for Spain's third city what Frank Gehry's Guggenheim did for Bilbao. But there are some key differences. First and foremost, Valencia is Calatrava's home town. He was born there, grew up there, studied there and even published a book on the city's architecture. And although his office is based in Zurich, Calatrava has been building in Valencia for most of his career. So just as Antoni Gaudí's curvaceous architecture has become synonymous with Barcelona, so Calatrava's could become one of Valencia's selling points.  The softly spoken 54-year-old is already something of a local hero, having risen to global prominence with projects like the Olympic stadium in Athens. His Alameda Bridge, crossing the bed of Valencia's dried-up Turia River, has been unofficially renamed "Calatrava Bridge" - it even appears as such on maps. But the architect's main preoccupation has been the City of Arts and Sciences, a vast, futuristic complex to the southeast. Conceived, by the regional government as a one-stop project to boost Valencia's profile, the 35-hectare park incorporates a science museum, a planetarium and other attractions, surrounded by pools and parks, and it was almost entirely designed by Calatrava. He has spent the past 15 years on it, and the Palau de les Arts, eight years in the making, is the piece de resistance - less his Guggenheim than his Sagrada Família.  Unlike Gaudí's overreaching cathedral, Calatrava has at least completed his grand plan. The Palau de les Arts unveiled itself to the world last October, with fireworks, royalty and an inaugural concert series, not to mention Calatrava himself, who declared that the €250m building was "on a scale with the cultural ambitions of the people of Valencia". It is one of the biggest performing arts centres in Europe. The architect has described it in nautical terms, alluding to the dried-up riverbed and the sea nearby, but it looks more like a gigantic Trojan helmet, or perhaps something Darth Vader might wear to a nightclub.  When it comes to Calatrava's style, again, Gaudí is a fitting comparison. Both architects have been labelled "organic", which means to say their work is short on straight lines and right angles, but both were less interested in imitating natural forms than divining their essential structures. Just as Gaudí worked out the curves of his buildings by making models in chains and hanging them upside down, so Calatrava takes his cues from horses' spines or the human body, and tests his ideas with sculptures as much as sketches.  In Calatrava's case, the result has been a unique architectural vocabulary that can only be described in terms of natural forms such as leaves, trees, animal skeletons, and birds. Full of soaring cantilevers, cavernous, uninterrupted chambers and elegantly tapered ribs and columns, Calatrava's buildings show off a great deal - hence his suitability for icon-making. And rather than clutter up his pure structures with cladding, he prefers to leave them bare, as unclothed demonstrations of his virtuosity. He seldom uses any materials other than steel, glass and concrete, and the colour of choice is white, with black or grey as a second option. Where Gaudí's buildings were warm and sensuous, Calatrava's are closer to the cool abstraction of Mies van der Rohe.  It is no understatement to call Calatrava a genius, but is he a genius of architecture? If there's a drawback to Calatrava's brilliance, it is that he thinks like a mathematician (his PhD thesis was on "the foldability of space frames"). There is often the suspicion with his work that the ingenious sculptural form came first and the job of fitting in actual people happened later. Unsurprisingly, his first major successes were bridges. The Alameda (or Calatrava) Bridge in Valencia, completed in 1995, is a classic example - a 130m span supported by a simple, flat bow along its middle that unexpectedly leans over at an angle to the vertical. The lean is to counterbalance the asymmetrical loading: there is a road on one side and a pedestrian path on the other. It simultaneously looks like something that shouldn't stay up and something that's impossible to refine any further.  From bridges, Calatrava graduated to transport infrastructure like train stations and airports (such as Bilbao), where his elegantly engineered forms fitted perfectly. But in recent years he's been struggling to expand his repertoire. The big commissions are still coming in - such as the train station at New York's World Trade Centre site, or a skyscraper in Chicago that will be the tallest building in the US - but so is the bad press. The last-minute completion of his ambitious Athens Olympic stadium was as tense a race as any that took place inside it. And his first project in the US, the extension to the Milwaukee Art Museum, spiralled over budget catastrophically.  To add to his woes, critics have begun to dismiss Calatrava's style as "kitsch" and to find his metaphors glib and unsuited to complex architectural statements. In this respect, Valencia's City of Arts and Sciences lays bare the architect's strengths and weakness like a biography. The simplest building is a trademark Calatrava promenade of minimal parabolic arches joined by leaf-like struts. Across a string of turquoise pools is the science museum - a vast hall resembling a dinosaur skeleton - and L'Hemisfèric, a regular dome covered by an elongated shell containing a planetarium and an Imax cinema. Reflected in the surrounding pools, L'Hemisfèric resembles an eye. Its sides even open up mechanically like an eyelid, albeit one dissected by the waterline. It's all startling, space-age stuff, but with its cold bleached bones, vast scale and relentless symmetry, this Calatravan monoculture can start to feel a little alienating.  The Palau de les Arts, though, is like a sigh of relief. It might not be as instantly iconic as his purer structures, but it's a good deal more inviting. The curved concrete plates on the outside are clad in white trencadís, that traditional mosaic of broken tiles so famously employed by Gaudí. There's even some blue in there, and some softening roof gardens. It looks like Calatrava is loosening up, and if there's a slight dad-on-the-dancefloor awkwardness - the "nautical" portholes along its flanks, or the giant mohican canopy, which smacks of dazzling engineering for its own sake - the Palau is still an extraordinary building.  Swathes of swirling white concrete channel the visitor through a procession of surprising, intriguing spaces, offering sudden views up to the sky or across the city. In the auditoria themselves, Calatrava's simplicity pays off, and simple wooden slats and coloured leather seats add touches of warmth. Even the architect's penchant for moving parts pays off: in the main theatre hall, the ceiling is made up of elongated light boxes that slide down to form a hi-tech curtain over the stage - nothing that will detract from the performances but a memorable piece of showmanship all the same. Calatrava has also opened up most parts of the building to the public, as part of a pedestrian route that connects two previously separate areas of the city.  It might not be his masterpiece but perhaps the Palau marks the beginning of a new phase in Calatrava's work, and a concerted attempt to correct his perceived weaknesses. Even if he retired tomorrow, his legacy is assured, but Calatrava still has plenty of time to develop. He has opened up previously uncharted realms of space and structure, and it remains to be seen whether anyone can fully exploit them, most of all Calatrava himself.
Santiago Calatrava's stunning buildings for Valencia bear comparison with the work of another great Spanish architect.  Steve Rose reports.