The MFA's New Art of the Americas Wing . . .

It's all about the art. It's not about the architecture. End of review—except for some persistent questions about museum design. Already judged a smashing success since its opening in late November, the $504 million, 121,307-square-foot Art of the Americas Wing at the Boston Museum of Fine Arts, designed by the London firm of Foster + Partners, does exactly what it was meant to do: This discreet addition at the east end of Guy Lowell's original 1909 Beaux Arts building houses a radical reorganization of the museum's American holdings, defined in the broadest possible terms.

Fifty three new galleries bring together the arts of North, Central and South America, spanning centuries and cultures. This vast expansion of the conventional definition of American art includes pre-Columbian artifacts, the museum's unparalleled American collection from the prerevolutionary period and the years of the Early Republic, examples of Latin American art and Native North American work from ancient to modern times, and contemporary American art through the mid-1970s. Embedded in these exhibition areas are newly refurbished period rooms. And while it is a questionable stretch to enforce a geographic and aesthetic logic on arts with totally different cultural roots and influences, the case has been well made in a handsome accompanying book, "A New World Imagined: Art of the Americas." Weaknesses revealed by the reorganization are acknowledged up front, with the promise of future acquisitions.

The new wing also adds a 12,184-square-foot, 63-foot-high glass-enclosed court that serves as a link between Lowell's classical building and the new four-story addition—a central pavilion flanked by two wings faced in the granite of the 1909 construction. The court provides a restaurant and space for social functions. The organization of the collection is chronological, from the most ancient cultures at the bottom to contemporary art at the top.

To carry out these changes, the museum broke up departments and lost longtime curators, actions that sent shock waves throughout the art world when announced by the museum's director, Malcolm Rogers, who came to the MFA in 1994 with strong ideas about updating and popularizing one of Boston's most respected and staid institutions. In 1999, he asked Foster + Partners to prepare a master plan for the museum's future that would include the new Art of the Americas wing.

Mr. Rogers made it clear that he did not want his new building to have a "showy outside." It doesn't. The best one can say is that the exterior is inoffensive. But Boston does not need architectural acrobatics to put it on the world map. Nor does it lack creativity, as demonstrated by Diller Scofidio + Renfrew's Institute of Contemporary Art on an undeveloped waterfront site. Unfortunately, the chance to use the MFA's new wing's tripartite division to reflect or reinforce Lowell's Beaux Arts symmetry within the modernist vocabulary has been finessed for a recessive solution of disappointing blandness.

The central pavilion showcases the most iconic examples of Americana, while the smaller galleries of the flanking wings are devoted to the art of other cultures, or a mix of paintings, furniture, decorative arts and wall coverings meant to convey the essence of the arts of a certain time and place. This practice, already in use in other museums, is particularly effective here because of the superb quality of the MFA's supporting material, much of it liberated from other departments.

If the basic concept is radical, the installations are traditional, but the best galleries are spectacular. All of the MFA's legendary knockouts are here—John Singleton Copley's incomparable Paul Revere portrait shown with Revere's famous Sons of Liberty silver bowl, a treasury of other Copleys and Gilbert Stuarts, and a roomful of John Singer Sargents, including his unforgettable "Daughters of Edward Darley Boit," complete with the actual, enormous Japanese vases that appear in the painting. But it is the portraits of the early patriots, statesmen and merchants—their likenesses executed with such painstaking realism and startling vitality that they seem to walk right off the walls—that bring history, and the galleries, to instant life.

Ascending to the next level, one is confronted with the increasing classical taste and European influence that shaped American painting and sculpture of the 19th century. A search for the "sublime" in nature coexisted with ambitious historical subjects, slick moralistic storytelling and an emphasis on technological virtuosity. Idealized nudes in uplifting allegories provided airbrushed soft pornography for the "refined" sensibilities of the time. Except for the genuine grandeur of the landscape school, the excess of pedestrian sentimentalizing is something only the most hardcore revisionist can really love.

Mr. Rogers has sidestepped this potential aesthetic booby trap by installing everything in the 19th-century manner—paintings "skied" on the walls, and sculpture filling the gallery as it would have been seen in its own day—a nonjudgmental approach that simply treats the work as part of our art and cultural history.

This leads us to galleries for the arts and crafts and aesthetic movements, the Beaux Arts and Deco periods, and American Modernism. This part of the story seems spotty and incomplete. There are outstanding pieces in every category, but the arts of mid-20th-century Modernism are obviously a work in progress, limited in range and routine in presentation.

The master stroke of the museum's reorganization is Mr. Rogers's own. His decision to reopen the museum's Huntington Avenue entrance in 1995 (closed since the construction of I.M. Pei's 1981 west wing) and the long-shut doors to the Back Bay Fens, part of Frederick Law Olmsted's "emerald necklace" parkland, predated and determined the Foster plan. It not only restored Lowell's original north-south axis, it re-established centralized access to both the existing galleries and the new wing through Lowell's great rotunda with its restored Sargent murals.

The new court, like all of Foster's work, is rational, corporate and cool. Designed for flexibility, there will undoubtedly be many opportunities for change. But the contrast with the covered court of the American Wing of New York's Metropolitan Museum, redesigned by Kevin Roche in collaboration with the chairman of the American Wing, Morrison Heckscher, and reopened in 2009, is both striking and instructive. The enclosing frame leaves open sky and park views. The MFA court is roofed with an extension of the uniform gallery lighting, making it feel totally enclosed. Even its exterior planting looks and feels remote.

In New York, the open space is surrounded by a wonderfully eclectic collection of 19th- and 20th-century American architectural artifacts. The facade of Martin E. Thompson's Bank of 1822-24, moved from Wall Street, forms the entrance to the galleries, with Louis Comfort Tiffany's exotic 1905 loggia for his own home, Laurelton Hall, across the way. Around the sides are an elaborate marble mantelpiece from the Vanderbilt mansion of 1881-83, a LaFarge stained-glass window and a filigreed Adler and Sullivan stair rescued from the Chicago Stock Exchange.

Selectively edited sculpture by Daniel Chester French, Augustus Saint-Gaudens, Hiram Powers and other Neo-Classical and Beaux Arts artists occupies a raised platform in a setting of fountains and greenery. Saint-Gaudens's elegant Diana perches gracefully on one foot above it all. Glass-fronted balconies offer tantalizing glimpses of American crafts. Curved marble benches designed in the classical spirit, and a small restaurant on the park side, offer rest and refreshment. As Mr. Heckscher explains, "this is architecture in the cause of art."

At the MFA the orderly, disciplined plan came first. Working in close collaboration with the Foster team headed by Spencer de Grey and Michael Jones, what Mr. Rogers got was a well-wrought container that accommodates his program perfectly. There are no subtleties or surprises, no risks taken. The new wing is an unassailably logical solution, superbly executed and singularly lifeless, largely redeemed by curatorial and installation expertise. The MFA's collection of early Americana would be wonderful anywhere, in any kind of setting.

Just don't expect that extra dimension of wonder and delight that architecture can add to art. Foster interiors are increasingly sleek and formulaic. Mr. Pei's 30-year old west wing, surprisingly undated, does so much more with so much less; it upstages the new addition creatively with passages like the daylight-flooded, curving pedestrian promenade under a barrel-vaulted skylight that forms a warm and pleasurable link between the museum's social and aesthetic functions.

The part of me that delights in and always hopes for the unique spaces and transitional experiences, the transformative light and views, the miraculous experience of art and architecture together, will not be sorry if Foster's master plan, which includes still another covered court, remains on paper, like so many ambitious expansion plans of the past.

Ms. Huxtable is the Journal's architecture critic.

By ADA LOUISE HUXTABLE