How much is gained by a museum renovation that offers twice the riches of the original but only half the magic? That’s the question I asked myself as I walked through the new Morgan Library, which reopens to the public on Saturday.

I have sorely missed the Morgan, which was closed for three years while it underwent extensive renovation and expansion. From the moment I first discovered the strange cluster of neoclassical, Italianate, and Victorian buildings at 36th Street and Madison Avenue, and the treasures housed there, it was one of my favorite places in New York.

Granted, the Morgan was never perfect. A pieced-together campus, its galleries were generally small and disjointed, but it had an old-world, mom-and-pop personality and charm. Unlike other museums, which “present” works of art, the intimate, maze-like Morgan Library demanded and rewarded in equal and mysterious measure. Entering through the small foyer on 36th Street and traveling deeper into the Morgan’s belly, with its cryptic hallways, dark corners, quick turns, and sudden, lavish surprises, provided a unique experience. As the library’s spaces and objects gave up their secrets and ghosts, it felt as if you had stumbled into Ali Baba’s cave.

Things have changed considerably. And there is good news and bad news.

Clearly, much has been gained with the $106 million renovation and expansion spearheaded by the Morgan’s director, Charles Pierce Jr., and designed by the Italian architect Renzo Piano. On the ground floor, Pierpont Morgan’s study has been relieved of its oppressive ropes and stanchions, finally freeing viewers to get nose to nose with the objects and paintings on display. Located downstairs are a new education center and a grand, new concert space, the Gilder Lehrman Hall. A beautiful, deep, and vertiginously steep performance space filled with red, plush seats and American cherry wood, the hall can seat 280 people and will principally host concerts, readings, and lectures related to the Morgan’s collections. And there are also a new cafe, a dining room, expanded book and gift shops, conservation space, reading room, and a reinforced vault to protect the Morgan’s holdings.

Most important, the Morgan now has twice the exhibition space in which to display a greater portion of its more than 350,000 precious objects. Currently on view, under the umbrella title of “Masterworks From the Morgan,” are seven breathtaking (and, by Morgan standards, large) exhibitions that together comprise more than 300 objects from their permanent collection. Here are drawings, Mesopotamian cylinder seals, illuminated manuscripts, sheets of music, printed books and bindings, and medieval objects from the Morgan treasury. Among the numerous masterpieces on view are two of the Morgan’s three Guttenberg Bibles, the “Lindau Gospels,” “The Beatus of Liebana,” the “Stavelot Triptych,” and drawings by Cezanne, Delacroix, Durer, Bernini, Raphael, Leonardo, and Michelangelo.

Yet something essential is missing from the installations: The works of art no longer feel integral with their surroundings. Compared to the spacious, airy, light-filled entranceway and lobby of the museum, they feel set aside or downright entombed. This is not a curatorial but rather an architectural problem.

The prevailing trend in museum renovation and expansion is to make art institutions as welcoming and accessible as possible. It’s as if getting people in the door and making art easily available to them are more important than their experience within the galleries. A lot of attention and space are given to entranceways, education programs, and electronic gadgets (a suite of computers now graces the Morgan’s lobby),as well as to dining, entertainment, and shopping.

In the name of community outreach, we have seen the neoclassical facade of the Brooklyn Museum butchered, its entranceway gutted, and its installations turned into theme-park displays. At the Museum of Modern Art, where we have witnessed an enormous increase in exhibition space, the new installations make the permanent collection appear smaller and less significant than they were before. The addition of MoMA’s expansive great hall – a noisy echo chamber that dwarfs the museum’s largest paintings and sculptures – has proved to be unfriendly both to crowds and to art.

The Morgan’s entrance has shifted from the small, relatively quiet entrance on 36th Street to a large, wide, glass one on busy Madison Avenue. The old entrance, which was elevated by steps and behind solid, heavy doors, may have been cramped, but it was never stuffy. It brought you from the everyday realm of the street to the intimate, hushed realm of a library.

As with traditional courthouse steps, cathedral steps, and museum steps, the Morgan’s elevation served as a reminder, both actual and metaphoric, of the change from lower to upper and from outer to inner; it always brought with it whispered voices in the entranceway. If you were not quiet, a stern older woman who sat at a table just inside the building reminded you that you were in fact in a “library.” Everything was as it should be.

The new entrance to the Morgan is only slightly sloped upward from the street. Like the entrances to the Brooklyn Museum and MoMA, it breaks down the distinction between city and museum. The doors are all glass: Buses and cabs seem to be driving right through the entrance hall.

The vast, soaring, light-filled, modern box of a lobby, made almost completely of glass, will undoubtedly inspire chatter and excitement. And, because its scale offers no sense of transition between smaller galleries and expansive lobby, the space will exert a magnetic hold on visitors. In the lobby, they will immediately smell the food in the nearby cafe, which shares space with the entrance hall. And the first steps they will encounter will be ones that, to the left, rise up to the dining room and gift shops – a set of beautifully restored rooms that encourage leisurely browsing.

Simply put, the new and improved, user-friendly Morgan is more mall than museum. Messrs. Pierce and Piano have greatly increased the Morgan’s physical amenities, both for visitors and staff, and they have left many of the galleries as they were, but they have spiritually wrecked the museum. A holy place forced into commercial submission, it is now hollow, soulless, and scattered.

It’s as if the Morgan family had finally packed up and moved out. Pierpont Morgan’s over-the-top yet personal library – which is lined with thousands of rare books, and has an iconographically rich, painted ceiling, a mammoth fireplace, stained glass, and a catwalk accessed through a hidden doorway – once served as an exhibition space. Changing exhibitions of books, manuscripts, choir leaves, letters, and book bindings filled the space, inviting visitors slowly to take in the room along with the objects on view. Now, viewers are greeted by a handful of objects in a vacuous, uninviting space that must be accessed as if it were a garage off the kitchen.

Morgan’s library and study, as well as the galleries, have been reduced from living and viewing spaces, where art and architecture thrive together, to mere period rooms and cold galleries. I greatly applaud more exhibition space, but the heart of the Morgan, which used to follow you wherever you went, is now firmly located in the huge, bland, steel-and-glass megalith of an entrance hall. The museum, now riddled with confusing doorways off the great hall, has lost its sense of mystery, flow, and cohesion. The library, study, and galleries have become mere tentacles of the octopus – the super-size lobby.

Mr. Piano’s lobby will accommodate large groups of people. There they can watch as glass elevators – their thick, black, tail-like cords dangling as they rise and fall through clear glass shafts – shuffle people from floor to floor with futuristic precision. They can stand on the seemingly floating, crow’s-nest platforms and stare down at the tops of indoor trees and the heads of cafe diners.

Functional beauty aside, Mr. Piano’s pavilion is not a piazza in which the public will gather to discuss art. It is not even mainly a holding tank for noisy school groups and long queues of people shaking out their umbrellas. The Morgan’s new entranceway and courtyard is a celebration not of art but of a superstar architect – of money, power, and what it can buy. It is the brand-name museum equivalent of those “great rooms” in which bigger is better, in which the function of the windows is to let people look in as much as out. The Morgan’s lobby is mainly a vast party space for wealthy museum patrons, donors, and benefactors who can, as they sip martinis and read their names etched on the walls, look around them, and say, “This is partly mine, all mine.”

“Masterworks From the Morgan” on view from April 29 (225 Madison Avenue, between 36th and 37th Streets, 212-685-0008).