The completion of the magnificent New Greek and Roman Galleries at the Metropolitan Museum of Art is one of the highest contributions to the New York art world in recent memory. The Met is considered to be the greatest museum in America. Tomorrow, when it opens to the public this “museum-within-a-museum” — comprising more than 57,000 square feet devoted to more than 7,500 ancient Greek and Roman artworks — the Met will ascend to a new place on the world stage.

The Met’s $220 million, 15-yearlong renovation and reinstallation of the original McKim, Mead, and White atrium entirely changes the way visitors will experience the museum, and it also re-establishes the bar for museum expansion. Overseen by the Met’s chief curator of classical art, Carlos Picón, the renovation represents a mindset — a classical vision — that emphasizes the experience not of museum architecture, but of art within museum architecture.

So rare in recent museum expansions and renovations, Mr. Picón’s vision allows for nothing to be sacrificed and everything to be gained. Art, architecture, and the city (through window views of the Met’s facade, Fifth Avenue, and Central Park) blend seamlessly and dance together beautifully.

Arranged chronologically from Prehistoric and Early Greek to Late Roman art, the installation begins, as it has in recent years, in the barrel-vaulted central grand hall and adjacent galleries just off and south of the Met’s Great Hall. It continues south beyond the 12-foot-high “Portion of a Column From the Temple of Artemis at Sardis” (c. 300 B.C.E.) to the 11 galleries including the newly renovated, fully skylit, two-story atrium that until recently was the museum’s boisterous restaurant. The additional galleries include the mezzanine’s intimate Etruscan area and a changing Study Collection filled with dozens of vitrines crammed full of smaller Prehistoric to Late Roman objects. Completely absent is the kind of dry, art historical “this-begot-this-begot-this” setting so prevalent in some museum installations. And also gone is the Grand Central–intersection atmosphere in the galleries, as well as the obtrusive gift shop, restrooms, and distractions caused by the restaurant’s lines, smells, and noises.

Considerably larger and more spaciously arranged, the Met’s collection of antiquities is reborn. The increasingly light-filled descent into the Greco-Roman wing, seemingly both stranger and more familiar than its earlier incarnation, takes you deeper, broader, and more richly into our classical past. Understated yet grand, airy yet interactive, and bathed profusely in natural light, the artworks have been placed with such care that Greco-Roman naturalism takes on a kind of town-square insouciance. The statues, columns, and objects do not feel staged. They interact with one another, exuding a newfound lyricism and lightness. They draw you nearer with their come-hither curves, smiles, cocked hips, and flowing drapery; and they bounce you from object to object and across galleries with the kind of aplomb that keeps sensations and images alive from the first gallery to the last.

Granted, natural light makes all art live and breathe. And I do not want to understate the sheer beauty of the color range — from white marble to ivory to yellow ocher, from Pompeii or “Red-Figure” red to turquoise blue to bronze-patina green — now present in the galleries. But more is going on here. Within all this natural light, I sense a curatorial playfulness and freedom that the smaller spaces did not allow.

In nearly every gallery is a centerpiece or a focal point, around which the other objects dance. A contemporary large, round, black marble fountain, pan-shaped and gurgling a foot-high burble, occupies the center of the new Leon Levy and Shelby White Court. Styled after a Roman villa courtyard, the gallery is the largest and most arresting of the new spaces. Here is a sense of expanse and reach, as well as mirroring and flanking. We experience weights, textures, torsions, turnings, and strivings in the sculptures, architectural fragments, and sarcophagi. The statues appear to be responding to one another and to echo or to answer movement with movement. And those movements unfurl through the space — carrying us from Hercules to Eros to Aphrodite.

Among the thousands of objects on view you will find old friends and thousands of new acquaintances. One can forget just how substantial the Met’s collection of Greco-Roman antiquities actually is. Masterpieces such as the “Kouros,” “Old Market Woman,” “Sleeping Eros,” “Relief With a Dancing Maenad,” “Girl With Doves,” “Statue of Pan,” “Etruscan Chariot,” “Panathenaic Prize Amphora,” and the “Vase in the Form of a Cockerel With Letters of the Etruscan Alphabet” are all featured prominently. Yet it is often in the groupings of objects that the sheer greatness of the Met’s collection soars. Lines of portrait busts, coins, cameos, jewelry, reliefs, grave stele, even Etruscan bronze fittings from a chariot, left me weak-kneed and awestruck.

Yet spatial vastness is not the only asset of the Met’s New Greek and Roman Galleries. It is often in the corners and in the more intimate areas and arrangements of objects that I sensed the monumental achievement of this renovation. Among the major additions to the new installation are the many breathtaking wall paintings from villas near Pompeii, including the restoration and reinstallation of the Met’s two bedrooms: one a bustling profusion of reds, ochers, and greens, and the other a somber study in black and gold. Both can now be entered freely, and both offer interior spaces that can take you as far inward as they can back in time.

At the Met, the naturally lit galleries — a strange combination of internal and external spaces — feel like newfound entries into ancient origins. In the museum’s new garden of marble, bronze, terra cotta, and limestone, Greco-Roman art does not read as the classical seeds of Western civilization but, rather, as ripe fruit, full blossom, and crawling vine.

Opens April 20 (1000 Fifth Ave. at 82nd Street, 212-535-7710).