After nearly 40 years of dithering and disaster, they finally got it right.

The new plaza in front of the General Motors building on Fifth Avenue at 59th Street is a triumph of urban design. It consists of a flattened area paved in pale gray granite that is raised one meter above the street and adorned with two reflecting pools and six honey locust trees. These flank the dazzling Apple store that rises up as a 32-foot cube fashioned from sheer glass. Suddenly, as if out of nowhere, New York has a new public space that will prove to be a source of civic pride and aesthetic delight.

Ever since the destruction of the Hotel Savoy, which lorded over this corner of Manhattan from 1905 to 1968, there has seemed to be something ill-fated about this most prominent of public spaces.The successive waves of tastelessness that washed over the site did not discourage the suspicion that it might just be cursed.

General Motors agreed to construct and maintain a public plaza in exchange for permission to build a skyscraper on the site in 1968. Though no one would ever claim that the resulting over-sized shaft was Edward Durrell Stone’s masterpiece, it proved to be better than the graceless suburban mini-mall that occupied its sunken forecourt, a space whose only memorable feature was a half-acre of windswept Astroturf.

Some seven years ago, along came Donald Trump, who, notwithstanding his well-earned reputation for goofy grandiosity, at least made an honest effort to improve matters. What resulted was a plaza whose main redemption was that it was above grade,rather than in the basement of the GM Building. It worked as a public space for the simple reason that the citizenry seemed happy enough to be there.

Unfortunately, its design was inept from every angle. Nor was it helped by that immodest slathering of marble and fools-gold that the Donald seems to favor and that transforms everything he touches into the Jacuzzi room of the Playboy Mansion. And even with all the people sitting happily around its fountains and planters, it could never shake a certain forlornness that was caused by the perennial inability to rent any of the commercial space below grade.

By 2003, the building and the plaza were on the block again, and this time the buyer was Macklowe Properties. There was little reason to trust that they would create anything worthwhile in the plaza, especially after seeing what they did this past autumn to the GM building’s three-story base – which extends all the way from Fifth Avenue to Madison Avenue. Whereas the building’s shaft is composed of emphatically vertical pinstripes, the base was tactlessly reconfigured with horizontal lines in a different material and a far inferior style. What had once seemed like a substantial counterweight to that soaring shaft now has all the immaterial impermanence of a party tent.

That outrage has been largely offset by the new plaza. It is clearly modeled on the marvelous space that Mies van der Rohe designed in 1959 for the front of the Seagram Building. But the outcome is, if anything, even better: Whereas the Seagram Building is surrounded by the middling towers of Midtown, this new plaza looks over the incomparable vista of Central Park.

There is also the miraculous aptness of putting an Apple flagship at this site. Despite its prominence, the location is not a natural choice for a retail outlet. It needed as a tenant an enterprise so big and so famous that it can afford a site that will serve primarily as a three-dimensional advertisement for itself. Perhaps no other corporation on the planet would have fit the bill as well as Apple, which has succeeded in branding itself as a lifestyle, even a state of mind.

Designed by Peter Bohlin of Bohlin Cywinski Jackson, the sheer glass cube carries into the realms of architecture the clean, minimalist perfection that graces Apple’s desktops, laptops, and iPods. Just as these physical implements of leisure and creativity conceal all manner of hidden complexities, so the commercial core of the new flag shipexists entirely below grade. Indeed, the cube is nothing more than a grand entrance: You descend into the predictably clean and minimalist retail space either through a glass walled elevator or a staircase that spirals downward along glass steps cantilevered along the elevator shaft.

The dark wooden boards that covered the construction site for the past six months have only just come down, and I have assessed the new space only in the splendid light of a fine May morning. It will be fascinating to observe how the store and the surrounding plaza are transformed in the shifting light of day, how they behave under clouds and in the change of seasons. Perhaps best of all will be the way this flagship – which will be open 24 hours a day – rears up, a luminous and unanticipated mirage, in the dead of night.