Audiences at the New York City Opera’s new production of Purcell’s “King Arthur” may go home thinking that opera was not a very well developed art form in 17th-century England. They would be right. Instead of writing operas, Purcell and his contemporaries wrote “semi-operas,” works in which music was grafted onto a spoken play, usually a pre-existent one in a specially prepared version. Still, the reality is rather different from what the exuberant Mark Morris spectacle, which had its premiere Wednesday evening at the New York State Theater, might suggest.

Revivals of semi-operas in something approaching their original form can be cumbersome for modern audiences, but Purcell’s music is of such superb quality that producers are constantly looking for new ways to present it. Mr. Morris’s solution is to chuck the spoken play entirely, which in this case happens to be by John Dryden and, atypically, was conceived together with Purcell’s music as a unified work. What is left in Mr. Morris’s version is a series of delectable musical numbers: songs, dances, duets, ensembles, and choruses, rich in musical invention and wide in emotional range. There are bawdy drinking songs and tender love songs, frankly erotic moments, and a heavy dose of British patriotism.

Mr. Morris gives it all a characteristically jubilant treatment, with a stage that displays constant action. There are characters in the guise of charming animals, a joyful maypole dance, a cute snow machine for the famous Frost Scene, and an amusing instance of simulated sex. Dancing by members of the Mark Morris Dance Group supplies a gloss on the music that is witty, energetic, imaginative, humorous, and just plain fun. Adrianne Lobel’s sets, which involve plain metal folding chairs and a background brick wall, are as audaciously sparse as Isaac Mizrahi’s costumes are audaciously motley.

But this ecstatic affair has a significant downside: Gone is any pretext of a plot to tie the pieces together. Discussions of “King Arthur” usually revolve around how it doesn’t deal with the Camelot story of Lancelot and Guinevere but instead with a conflict between Britons, led by Arthur, and Saxons, led by Oswald. This is all irrelevant here — because the main characters in a semi-opera perform only in the spoken play; they never appear in Mr. Morris’s version. Thus, this “King Arthur” presents sequences that lack any cohesive dramatic framework, instead offering abstract pieces involving singing and choreography. Purcell’s music, however, is usually praised for the way it is tied to and arises out of the drama. Wouldn’t it be interesting, for example, to know more about those inviting river sirens who cry, “Come naked in for we are so”?

Still, what Mr. Morris does, he does well, and that includes drawing performances from the seven solo singers that are as vibrant as those of his dancers. Sarah Jane McMahon’s bright soprano and vivid interpretation of the text made her first song, “Hither this way,” a delight, and she was also heard to fine effect in a duet for two lovers near the end, which found the baritone Alexander Tall in excellent voice. Soprano Mhairi Lawson, making her City Opera debut, was especially good in the Frost Scene (which arises in the play as a demonstration of Oswald’s magical powers), later offering a lucid if rather cool account of Purcell’s beguiling tribute to Britain, “Fairest Ile.” Another soprano, Heidi Stober, made appealing contributions to several duets. Steven Sanders, also making a City Opera debut, sang with a clear, healthy tenor, excelling especially in the irresistible pastoral song with chorus, “How blest the shepherds.” Among other duties, Daniel Mobbs emerged from a modern refrigerator to give an arresting account of the Cold Genius’s song with its brusque chords and halting manner imitative of shivering. Another debutant, countertenor Iestyn Davies, made a good impression in the song “I call you all to Wodan’s Hall.”

Unfortunately, Mr. Morris did not similarly lavish his directing skills on the chorus. Relegated to the orchestra pit, as it tends to be in his productions, the chorus was heard to acoustical disadvantage, which, given its importance in this piece, proves a major drawback. Conductor Jane Glover had the modern instruments of the City Opera orchestra sounding stylistically quite satisfactory in a reading that was thoughtfully shaped and vitally paced.