MORE than ever, composers are busily breaking down walls between stylistic categories. Opera in particular has been a poacher’s paradise. We have had folk opera, jazz opera and rock opera. Bono, who collaborated with the Edge on the music and lyrics of “Spider-Man: Turn Off the Dark,” called the show “Pop-Art opera.” Whatever that means. But of all such efforts, mixing opera with the Broadway musical might seem by far the most natural combination.

Then why are so many efforts to crisscross that divide so bad? For one thing, composers from outside the field often have a distorted understanding of what opera actually is. They borrow the most superficially grand, inflated and melodramatic elements of the art form, whereas opera is actually a richly varied and often tautly narrative genre of musical drama.

Consider “Séance on a Wet Afternoon,” the first venture into opera by Stephen Schwartz, the composer and lyricist of “Pippin,” “Godspell” and the long-running “Wicked.” “Séance” was presented this spring by the struggling New York City Opera. The promise here was that a leading musical-theater artist might bring fresh energy to opera. But Mr. Schwartz’s tepid, sappy score had little of the spark and originality of “Wicked.”

Another much-discussed production this season, presented by the Lincoln Center Theater, earnestly tried to split the difference between opera and musical theater: “A Minister’s Wife,” with a book by Austin Pendleton, music by Joshua Schmidt and lyrics by Jan Levy Tranen. It was adapted from George Bernard Shaw’s play “Candida,” about an officious minister with Socialist convictions, his ebullient wife and a dreamy, dangerous young man who idolizes her. As performed by a chamber ensemble and a small, gifted cast, the musical score was alluring and nuanced, with intricate ensemble numbers and long-lined melodic writing cushioned by lush orchestral harmonies and rippling figurations. But “A Minister’s Wife” seemed a precious piece: either pretentious musical theater or tame quasi-opera; take your pick. And with Mr. Pendleton’s adaptation of Shaw’s brilliant dialogue, the musical numbers sometimes felt superfluous.