Even if you’ve been to every Renzo Piano–designed museum of the last ten years, you may be surprised at how much there is to admire in his new Modern Wing at the Art Institute of Chicago. Though not without flaws, the addition is Piano’s best museum in America since the Nasher Sculpture Center in Dallas of 2003, and the best building in downtown Chicago since the John Hancock opened in 1970.

The Modern Wing, like the soaring Hancock, shows Chicago’s ambition. Conceived more than ten years ago, it ended up costing $294 million, and is likely to be the last great museum addition of its kind in America for some time. Its 264,000 square feet enlarge the Art Institute by a third and make it the second largest art museum in the United States. Chicago, no longer really even the “Second City,” is competing with New York again—at least in its mind, and that’s a good thing.

The addition allows the Art Institute to show off its encyclopedic collection, which includes its modern and contemporary art, such pieces as a suite of color panels by Gerhard Richter; two rooms for the gown, tissue box, and other odd objects and wallpapers by Robert Gober; and a gallery for the newly-acquired Hinoki by Charles Ray, a trunk of an oak tree on its side, hand-carved out of cypress. You can no longer think of the institute as a limestone building full of French Impressionist works. The wing is a game-changer.

Ten years ago, the Art Institute hired Pritzker Prize–winner Renzo Piano to design a smaller addition on the south side of the building. When Mayor Daley’s plans for Millennium Park, which was to cover over rail yards and parking lots downtown, grew to become Chicago’s most important project since the World’s Columbian Exposition of 1893, the Art Institute shifted its new addition to the north to face it. Accordingly, the Modern Wing grew in scope and cost.

Millennium Park, of course, features Frank Gehry’s band shell, waves of undulating stainless steel that reflect light and give the city pure joy. Piano said at the time that his building would engage in a “dialogue” with Gehry’s work, and it has. Gehry’s curving pavilion is directly framed by Piano’s rectilinear gallery windows; outside, Gehry’s steel reflects in the Modern Wing’s glass.

At the wing’s inception, an Art Institute trustee told me, “We’ll have to spend a lot of money on details; but if we spend the money, I know we’ll get a masterwork.” And so they did. The economic downturn after 9/11 didn’t stop the project. Having been called upon to fund Millennium Park, wealthy Chicagoans then ponied up for the museum so that for the first time in far too long, a grand civic monument could be properly conceived and executed in their city.

The detailing throughout the wing is at the highest level. From handrails to wooden floors to ventilation systems, the master architect got much of what he asked for.

The main sensation in the Modern Wing is its light. Piano’s system of louvers on the roof block the harsh southern light, admitting the calmer northern light, filtering it and diffusing it through vellum. The effect comes as close to perfection here as he has ever achieved, creating spaces that are alive yet serene. Looking up, the white aluminum blades are elegant and less fussy than Piano’s recent work in Los Angeles.

Moving the wing to the north side also allowed Piano to open that entire facade with floor-to-ceiling glass. This gives stunningly sensuous views of Millennium Park across the street, while the double-layer glass blocks the noise of the city. When you see people walking in the gardens across the way, it’s as if Piano has taken a masterpiece of the Art Institute—say, Seurat’s A Sunday on La Grande Jatte—and brought it to life.

Other works like Matisse’s large Bathers by a River gain in juxtaposition with the colorful gardens and water elements of the park outside. Constantin Brancusi’s reflective forms by the window engage with Anish Kapoor’s shiny, bean-shaped Cloud Gate outside, one of the great crowd-pleasing pieces of public art in the park. The south wall overlooking a new garden is also glass, covered with integrated thin scrims when it’s not overcast.

All Renzo Piano museum wings are similar but are not created equal. One may wonder why Chicago did so well. Years ago, I walked through the New National Gallery in Berlin with Piano. He was in awe of the place. It has minimal amounts of glass, steel, and stone, but is elegant, refined, and uplifting to the spirit. It was designed, of course, by Ludwig Mies van der Rohe, a German living in Chicago.

Piano brings some of that back to the Windy City. His exterior is boxy, glassy, and symmetrical like a temple, in the same way that Mies’ was. His slender, white-steel, tapering columns hold up a wafer-like flat white roof that extends out over the galleries; Piano calls it a “flying carpet,” and it’s part of his renowned system of getting natural light into galleries. The roof is Miesian, yet its horizontal thrust also recalls local hero Frank Lloyd Wright’s prairie style. The platonic cube of the main galleries, with ornament on the side, reminds one of Louis Sullivan’s Midwest banks. Like those, this is a jewel box that contains great treasure.

Piano deftly wove his building into Chicago’s history: He added parallel planes of Indiana limestone walls to complement the Art Institute’s beloved 1893 Beaux Arts building. Piano’s flat facade contains Millennium Park, and his transparent walls allow the grand urban square to transition gracefully from nature and pleasure to city and culture.

Yet not all is right at the Modern Wing. While the main building has a satisfying cube shape, other volumes have been messily added to the east side. First comes the nave-like entrance court, and then another is tacked onto that for more galleries and the restaurant. These feel arbitrary.

Moreover, Piano’s museum gives almost no views of Lake Michigan. Windows or a terrace on the east side would have offered spectacular views of Grant Park and the lake. The Modern Wing is a large intrusion into the “sacred” lakefront parks of Chicago; all the more reason to give back new lake views.

A 620-foot-long pedestrian bridge designed by Piano also mars the project. It blocks the facade, also seems tacked on, and is not well resolved where it meets the adjacent park. The bridge would not be necessary if city authorities had seen the wisdom of closing Monroe Street between the park and the museum, which would also help usher families into the museum.

Piano’s bridge again engages in a dialogue with Gehry, whose bridge in Millennium Park winds left and right like a river. Piano’s is a straight shot up from the park to a third floor sculpture terrace, free to the public, another stroke of civic generosity.

The Art Institute still straddles working train tracks. Part of Piano’s design was to open windows in the existing hall connecting the two parts. He wanted even larger windows, which would have been an improvement.

The museum is rightfully proud of its dignified yet intimate Beaux Arts entrance on Michigan Avenue, which makes Chicagoans feel like they’re going home when they go in, and that makes them feel like part-owners of the collection. Still, many will take Piano’s entrance to the north, which has a more commercial feel. It’s a large space: light-filled, double height, mall-like. Will this change the connection that the next generation feels to the place? Thankfully, the gift shop and cafe in this arcade are not front and foremost.

The Art Institute is seeking LEED Silver certification for the Modern Wing. For a city and a mayor that crow about being the “greenest” in America, a higher level of sustainability could have been achieved.

In the main, though, the Modern Wing is a triumph, with a civilizing presence. Piano has resolved the tension between what he calls a “beautiful fragility” and the need for strength. Power brokers in Chicago felt the city deserved an example of the world’s best contemporary architecture, and they got one.

Lifson and Piano discuss the new museum in an exclusive interview.

The secrets behind the museum can be found just below the surface.