When William Christie and Les Arts Florissants presented Lully’s “Atys” at the Brooklyn Academy of Music for the first time, in 1989, it was as if a curtain had been pulled aside to reveal an alternative operatic universe. The work was so different in sound, spirit and look from the 19th-century Italian operas that dominate the mainstream opera world that it seemed almost a different art form.Sure, everyone knew that French Baroque opera was staged with greater opulence, sung with a distinctive suaveness and packed with courtly dance, but seeing what that meant, by way of a 1676 work known to be a favorite of Louis XIV, hammered home its differences and made lots of converts. Since then Mr. Christie and company have returned with similarly revelatory productions of other works, but that 1989 “Atys” (and a revival in 1992) has retained its place on my own list of favorite musical experiences.Thanks to a $3.1 million gift from Ronald P. Stanton, a businessman and philanthropist who feels similarly about the production, the academy brought back “Atys” to open its 150th-anniversary season on Sunday afternoon. The staging, by Jean-Marie Villégier, is unchanged, though Carlo Tommasi’s set (a single, full-stage room with black and gray marble walls) and most of Patrice Cauchetier’s ornate costumes and wigs (mostly Sun King chic with variations to suggest mythological times) have been freshly remade.“Atys,” with its libretto by Philippe Quinault, is based on Ovid’s tale of love between mortals and gods gone awry. Atys, supposedly indifferent to love, has fallen for Sangaride, who is about to marry Célénus, the King of Phrygia, and though Sangaride sees the benefits of the match, she loves Atys. The goddess Cybèle loves Atys too, and chooses him as her sacrificer, an office he abuses to break off the betrothal of Sangaride and Célénus. But as Cybèle warned Atys in an elaborate dream sequence, crossing the gods is unwise, and the final act is devoted to her revenge (and remorse).The opera, four hours long, is a stunning piece of theater, largely because Mr. Christie’s expertise in 17th-century French style, with its distinctive pacing and coloration, brings it so fully and vividly to life. Les Arts Florissants sounded as polished and flexible as ever, but the most striking aspect of the performance was the approach that Mr. Christie had his singers take.The production’s monumental aspects notwithstanding, this “Atys” is sung almost as chamber opera, or at least closer to what you hear in a relatively small house like Glyndebourne than at the Metropolitan Opera. From the top of the cast to the bottom, there was no forcing, no outsize projection. You had the feeling, illusory or not, that the singers were performing at speaking volume; in fact, the pianissimo passages that propelled Anna Reinhold’s portrayal of Cybèle, particularly in the final act, were among the production’s most thoroughly moving moments, and you did not have to strain to hear them.Ed Lyon’s portrayal of Atys, in the first three acts, had a deer-in-the-headlights quality that convincingly conveyed his character’s confused loyalties and amorous desperation. And he captured Atys’s moment of decisive boldness (and his undoing), in the fourth act, with equal success. He used his tenor to fine effect throughout, mirroring Atys’s tragic evolution in his vocal characterization.Emmanuelle de Negri, a soprano, matched that progression perfectly as Sangaride, and the interesting, sometimes gruff, texture of Nicolas Rivenq’s bass-baritone suited both the regal and outraged sides of Célénus’s music.“Atys” has a huge cast of supporting characters, some played by young singers in Mr. Christie’s Jardin des Voix training program. Most also contributed to the lustrous choruses that are among this work’s joys. And the Compagnie Fêtes Galantes executed the plentiful choreography by Francine Lancelot and Béatrice Massin with an elegance that was consistently riveting.