It’s hard to believe that Giacomo Puccini wrote an opera at the very height of his powers that has never quite caught on — except for one aria. La rondine ( " The Swallow " — as in " Fate is drawing you onward, like a swallow, to a land where dreams are fulfilled " ) comes late in his career. It was followed only by Il trittico — three one-acts — and Turandot, which he left unfinished, and it’s his most neglected mature work (in Boston, it was last staged in 1958). He composed it for Vienna in 1916 (but it had its premiere in Monte Carlo), and it’s the closest he came to writing an operetta. Its German-based libretto seems like something out of Arthur Schnitzler, the sophisticated Viennese playwright, knowing in the ways of love, whose Traumnovelle was the source of Stanley Kubrick’s Eyes Wide Shut.

La rondine takes place in the most Viennese rondissement of Paris. Magda, who’s well kept by the wealthy Rambaldo, dreams about a romantic, perfectly irreproachable two-hour interlude she once had with a young student, and despite glamorous parties and jewels, she still longs to recapture that rapturous innocence. Along comes Ruggero, the son of her protector’s old friend — a handsome, romantic, naive young man from the country who wants a taste of Paree. Magda’s saucy maid, Lisette, recommends a demi-monde café — the very place where Magda had her long-ago adventure. So Magda, dressed as a shop girl, slips away and meets Ruggero (who doesn’t recognize her), and they fall instantly and passionately in love to one of Puccini’s most luscious tunes.

They shack up on the Riviera. Alas, he comes from a " good country family, " so he wants to marry her. But with her past, how could she be anything more than his lover? So she must — because she loves him — part from him forever. It’s the plot of La traviata (and Camille), except with a healthy heroine. Puccini was never satisfied with the conclusion and kept rewriting the last act. On a recent PBS telecast, Magda goes off to drown herself.

The Boston Lyric Opera is giving us the original version (at the Shubert through April 8), in which Magda simply walks away — which is better, though it’s still unconvincing and melodramatic. Tragedy isn’t allowed in operetta. If only Puccini could have learned from Richard Strauss’s most Viennese opera, Der Rosenkavalier, which he admired, and in which, with poignant wistfulness, the Marschallin resigns herself to giving up her young lover. For two acts, Puccini captures a world of pleasurable indulgence. ( " Are you rich? " a woman asks a stranger at the café. " Sometimes! " he answers.) But he just couldn’t keep it light. Sex and happiness can’t co-exist. His heroine has to Suffer, to Sacrifice her One Chance for Fulfillment. " I can never enter your home, " Magda tells Ruggero. " I say goodbye as a mother to a son. "

Gimme a Freudian break! Puccini obviously didn’t have his heart in this turn of events — the music in the last act loses its freshness and becomes cloying and repetitive.

But the first two acts of La rondine are a delight, a riot of lush melodies, soaring waltzes, and that gorgeous dream aria ( " Chi il bel sogno di Doretta " ). And BLO gives the opera one of the company’s all-time best productions. John Conklin’s striking sets — a colorful, airy mélange of styles from art nouveau to art deco (an elegant drawing room with an on-stage piano, a bustling café, a villa on the Riviera) — came from the Opera Theatre of St. Louis, and they just fit on the Shubert stage. This production also marks the return of one of BLO’s few good stage directors, Colin Graham, who was last here nine years ago. His 1993 debut, with Berlioz’s Béatrice et Bénédict, featuring Lorraine Hunt and James Maddalena, has been one of BLO’s two smartest productions, the other being Stephen Wadsworth’s imported Handel Xerxes, in 1996 — also with Hunt. And this time, his blocking seems even sharper, more detailed, more elegant; his stage movements have an air of natural spontaneity (characters look at each other!) and, even rarer, reflect the music (Magda, for example, slides past some eager oglers on the steps of Bullier’s Café to a cascading harp glissando).

The cast is one of BLO’s best. Pamela Armstrong (Magda), who sings Puccini at the Met and Mozart at New York City Opera, is an appealing, sensitive actress of charm, intelligence, and (especially in her final exit) dignity. Her ripe peach of a voice has a seductive flutter in it. Opening night, she worked hard to hit what should sound like an effortless climactic high C in the soaring " Doretta " aria — it didn’t float out of time as it has done for some famous sopranos (like Kiri te Kanawa on the Room with a View film soundtrack). But everywhere else, she looked and sounded like a dream, and she made my heart ache for Magda.

In the role of Ruggero, tenor Shawn Mathey’s naive earnestness is thoroughly believable (though he has an uphill fight in that soggy last act), and his light sweet voice swells with lyric suavity and genuine tenderness. Baritone James Maddalena also makes a happy return as Magda’s generous sugar daddy. He’s in velvety, resonant voice, and in this small role he conveys a complex mixture of self-centeredness and sensuality, pride and pain.

Soprano Elizabeth Comeaux has done prima donna roles with BLO, but I prefer her cheeky, if vocally unsettled, soubrette in the secondary part of Lisette. Tenor David Cangelosi, who used to be in the BLO chorus and is now singing character roles around the country, plays the cynical (probably sexually ambivalent) poet Prunier, the satirical voice of the anti-romantic, who — to his shame — is currently infatuated with Lisette. Some opening-night observers felt he was absurdly over the top, but I thought he carried off his overstated gesturing and posturing with aplomb, and until his voice started to give way a little in the last act, he sang extremely well. Everyone sounded diminished by the Shubert’s dead acoustics.

Graham individualizes each of the smaller roles, so the stage is full of characters. Choreographer Gianni Di Marco (from Boston Ballet) has come up with some clever waltzes that a chorus of singers can dance without seeming klutzy. BLO music director Stephen Lord captures the crystalline delicacy of the score, its swooning waltzes and boulevardier sophistication. He obviously loves this music, with its throwbacks to Bohème, Butterfly, and Manon Lescaut and its hints of the more advanced harmonies of Turandot Chinoiserie. The orchestra is at its most gracefully attentive.

BLO has a history of disappointing, often misguided productions of great operas, but by remaining faithful to the spirit of Puccini’s music and getting the best people, the company proves it’s capable of doing a stylish production. Next year’s so-called " Italian season " is a retrenchment — only three operas, unadventurous ones, by the most popular composers: Verdi’s Rigoletto, Puccini’s Tosca (conducted by Keith Lockhart), and Mozart’s Cosí fan tutte (conducted by Charles Ansbacher), on the heels of this season’s Rossini, Mozart, Puccini, and imminent Johann Strauss. The company once promised an American opera every season. Is conservative programming really the only way to sell tickets? A late friend of mine used to say: " When all else fails, try quality! " Maybe that’s the only name brand necessary to make people want to come.

THE JAZZY AND THE BARDIC were primary colors in Collage New Music’s latest program. Music director David Hoose led two world premieres by Boston-area favorites Richard Cornell and Andy Vores and a 1996 Collage commission, Spring Fever, by the 82-year-old Andrew Imbrie. New music, Hoose told the audience, has often been full of special effects. But the new music at this concert was going to be devoted to traditional things like " pitches, rhythms, dramatic purposes, emotional interests, and narrative sensibility. " The strangest sound we were going to hear would be Judi Saiki Couture tapping on the frame of her harp.

Cornell’s New Tropes, in three short movements, all of which end quietly, begins with a harp (the bardic element) and a quiet underpinning of tribal drum beats (percussionist Craig McNutt); that’s followed by a slow section for moody winds and strings. A beautiful oboe song (Peggy Pearson) — almost blues — opens the next movement, with a series of iridescent variations, including imaginative uses of tambourine, a jazzy drum set, and a passage something like the Chordettes singing " Mr. Sandman, " with a different instrument making up each note in the tune. Cornell calls the last movement " meditative " ; I found the shivery gongs quite eerie, too.

Spring Fever swells the ensemble from eight to 10 players. It’s a denser, more angular piece, also in three movements, opening in darkness and winter and ending with a big bang in a new season of rebirth. Piano riffs (Chris Oldfather), another bluesy oboe lament, and witty syncopations (DAH-ta-ta-DAH, DAH-ta-ta-DAH) whiz by. There’s never a moment when something isn’t engaging your attention.

Vores’s Goback Goback is a setting of eight poems by the almost forgotten 20th-century Cornwall poet (born in Scotland) W. S. Graham. These are works that deal with the contrary pulls of returning to a ghostly childhood and trying to live more fully in the present. Several of the poems remind me of the folk songs Mahler uses in his Des Knaben Wunderhorn cycle: " How would you like to be killed, " says the mysterious voice at the beginning of " The Visit. " The title is the call of the grouse in the last poem, both a seduction and a warning.

Goback Goback also begins with a harp, and here the bardic element is most explicit, reinforced by strumming strings, staccato beats, and snaky, slithery winds. In a marvelous interlude between the second and third sections, plucked cello (Joel Moerschel) and rhythmic bass (Jim Orleans) dissolve into ravishingly lyrical strings.

Vores’s striking music conjures up the ghost worlds of Schumann, or Mahler, or Benjamin Britten, only on hallucinogens. " Imagine a forest,/A real forest, " another poem begins, and the music wants to surround us in dark woods, submerge us in a fathomless sea, disintegrate us into an ephemeral cloud. And it captures Graham’s creepy comedy ( " Dear Bryan Winter " begins, " This is only a note/To say how sorry I am/You died " ).

Baritone David Kravitz was the eloquent singer, conveying the sense that he knew what lurked behind the words and letting us hear every syllable. David Hoose led every piece with passion and precision. And the playing seemed flawless. It’s a rare new-music event that makes me want to hear each piece over again. And again.