On the morning of 20 November last year, the queue snaked round the block for well over an hour before the Museum of Modern Art (MoMA) reopened its doors after being closed to the public since June 2002.

A cynic might observe that for this day only, visitors could avoid the $20 adult admission fee that makes MoMA the most expensive museum in the US. Even so, the anticipation aroused by the 'new' MoMA was palpable. According to the director, Glenn Lowry, the museum had not just been rebuilt, but reinvented.

Not for the first time in MoMA's 75-year history, the extension of its footprint on the Manhattan city grid has been used as a catalyst for institutional renewal and for a lever to refinance the organisation. The architect charged with the latest process of physical transformation was the Harvard-educated Japanese modernist, Yoshio Taniguchi.

So just how different is the revamped MoMA from its predecessor? Most obviously, it is much bigger. The chance to buy a group of buildings next to the previous museum site means the galleries now extend across the whole block from 53rd Street to 54th. Today, MoMA is almost twice the size it was in 2002, although the relative increase in gallery space is rather less - from just under 8,000 to 11,600 sq metres.

Taniguchi is reputed to have told MoMA: 'If you give me enough money, I'll make you a beautiful building. If you give me more, I'll make it disappear.' In the event, a building budget of $425m (£220m) seems to have been sufficient to pull off his disappearing trick, by providing the museum with an austere extension that elegantly picks up the modernist thread of MoMA's architectural history and blends into the corporate cityscape of midtown Manhattan. Designing a museum to look like an office block was radical in 1939 - 65 years later, it looks conventional.

By awarding the architectural competition to Taniguchi, in preference to contenders such as Herzog and de Meuron, Rem Koolhaas and Bernard Tschumi, the MoMA trustees clearly voted in favour of institutional continuity rather than architectural rupture. What they bought was an homage to the right angle, constructed of glass and steel, and clad in black Zimbabwean granite.

The core of the new MoMA is Taniguchi's six-storey gallery block, above which are a further ten floors of offices. Entering through the sleek, street-level lobby, visitors are oriented towards a glazed curtain wall looking over the restored Sculpture Garden. From here a staircase takes you up to a top-lit atrium on the first floor that rises up through the centre of a five-storey stack of collection and exhibition galleries.

For Taniguchi, the passage from street to gallery is important - the absence of an escalator to the first floor is designed to slow visitors and to preface their experience of the art upstairs with a view of the Sculpture Garden against its urban backdrop. This is characteristic of Taniguchi's strategy to open out the museum to the city, while also creating an interior architecture that is more porous and permissive than the cramped, prescriptive route through art history that was dictated by the previous layout.

Daylight enters Taniguchi's block through the atrium and the picture windows which reconnect the museum with Manhattan. Inside, the massive height of the atrium dwarfs a display of art that includes an incongruous juxtaposition of Barnett Newman's Broken Obelisk and a version of Monet's Water Lilies.

More successful is the way in which Taniguchi inserts internal windows, balconies and landings into the towering walls of the atrium, simultaneously tempting and inviting visitors to enjoy its vertical dimension. Again the architecture is more assured than the display - a glimpse of The Dance by Matisse through an upper window is tantalising, but its position at the top of a stairwell isolates it from the rest of the collection and makes for awkward viewing.

Taniguchi's gallery suites offer visitors a more fluid and complex path through the histories of modernism than MoMA's previous trademark 'beads on a string' approach. Most of the galleries have more than two exits - the inviting vista of rooms to the right and left is a deliberate temptation to short-circuit the chronology of the displays or to follow a parallel track through 20th-century art.

In spite of Lowry's insistence that this hang is just anotherr experiment in unfolding the meaning of modern art, and that MoMA is more laboratory than museum, there is a compelling insistence in a collection that contains key works such as Cézanne's The Bather, Picasso's Les Demoiselles d'Avignon, Pollock's One (Number 31) and Jasper John's Flag.

These are the paintings on which both the logic of the collection and the status of the institution hinge - they embody the transformation of economic wealth into cultural capital that is at the heart of the new MoMA.

The same well-mannered architecture houses MoMA's rich collections of photography, prints and drawings in suites of more intimate and subdued galleries. Each of these is the domain of a curatorial fiefdom that continues to preserve and display the visual culture of the 20th century in discrete compartments.

Architecture and design occupy a more prominent position in the building but barely speak to each other, let alone the other collections. So much for the spirit of experimentation.

Invariably, each gallery in the new MoMA is named after those donors who have made such a substantial contribution to the total redevelopment budget of $858m. The trustees alone contributed a staggering $500m to the project.

This is the reality of MoMA 2004 - an immaculate and expensive new building that is perfectly suited to house the corporate headquarters of one of the richest, most glamorous and most conservative museums in the world.

Helen Rees Leahy is the director of the Centre for Museology at the University of Manchester
The house that Rockefeller built

The name Rockefeller runs through the Museum of Modern Art's (MoMA) history like a stone pillar. Abby Aldrich Rockefeller was one of the three women who founded MoMA in 1929.

Three years later her husband, John D Rockefeller Jr, provided a home for its expanding collections in a limestone townhouse on 53rd Street. The Rockefellers also owned houses on 54th Street that were demolished in 1939 to accommodate the creation of the museum's Sculpture Garden.

The foundations and architectural rubble of these Rockefeller houses remained buried beneath the surface of the Sculpture Garden until 2000, when the site was bulldozed prior to its restoration and incorporation into Yoshio Taniguchi's new museum complex.

Enter Mark Dion (pictured), the artist who recovers lost histories and creates unexpected juxtapositions from the detritus beneath our feet. MoMA commissioned Dion to conduct one of his archaeological 'excavations' - in fact, a kind of building site scavenging - while the site was being turned over prior to the construction.

The result is an engaging installation entitled Rescue Archaeology: A Project for the Museum of Modern Art, in which Dion exhibits recovered mantelpieces, scraps of wallpaper, tiles and shards of marble that once decorated the fabulous Rockefeller houses. Now they are exhibited by Dion in a basement gallery in the new MoMA as a sweetly ironic reminder of where it all started.

Today, Abby son's, David Rockefeller Sr, is the chairman emeritus of the MoMA board and one of its most generous benefactors. Taniguchi's new wing is named after him and his wife, Peggy. No surprise there.

But one of the puzzles of the new MoMA is the choice of Paul Signac's portrait of the dealer and art critic Félix Fénéon (replacing The Bather by Cézanne) as the opener to the paintings collections. Answer: it belongs to Rockefeller.