Don't pop the cork just yet. There are a number of reasons to toast the return of John Guare and Mel Shapiro's musical adaptation of Shakespeare's Two Gentlemen of Verona to the Delacorte, where it got its start 34 years ago. But this amiable new production of the show (with music by Galt MacDermot and lyrics by Guare) is not all cause for celebration.

Make no mistake: The show itself is a jubilant, warmhearted musical comedy that Shakespeare himself could be proud of. And it so sets its sights on entertainment that audiences today can be proud of it, too - its effortless ability to please should make faux frivolities like Dirty Rotten Scoundrels and Spamalot blanch.

But the overall atmosphere of the production, which is directed and choreographed by Kathleen Marshall, is one of a surprise party that the guest of honor was warned about in advance. There's no end to the merriment onstage, but so much of it is of the forced, artificial variety that you're propelled from beginning to end merely by the hope that you'll eventually be jolted back to theatrical reality.

That only happens when Norm Lewis and Renée Elise Goldsberry are at the center of the action. The two don't share the stage until near the end of the first act, but when they do (in the back-to-back songs "To Whom It May Concern Me" and "Night Letter"), its enough to put Central Park on temporary fire alert.

Goldsberry's Silvia, the daughter of the Duke of Milan, arrives at the letter-writing shop of Lewis's Valentine to send a missive to her beloved Eglamour, that he might rescue her from her arranged marriage to the wealthy Thurio. Goldsberry, reclining and writhing over Valentine's desk, is the picture of lurid, lusty desperation, a woman who'll give anything to get what she needs, and practically does. When her wiles become too much for Valentine and he acquiesces to her demands (and her love) and they sing together, Lewis and Goldsberry are the closest thing to musical theatre royalty New York has seen since Nathan Lane and Matthew Broderick left The Producers.

It's far more difficult to get involved in the companion story of Proteus (Oscar Isaac), Valentine's friend, who stays behind in Verona to court and make love to the beautiful Julia (Rosario Dawson), but is sent to Milan by his father. Julia, pregnant with his child, soon pursues him with her friend Lucetta (the ebullient Megan Lawrence), the two dressing up as men to protect their identity and what's left of their virtue. The spunky Lawrence pleases in her worldly wise role, but neither Isaac nor Dawson possesses a blaze-setting singing voice or a personal magnetism capable of filling the Delacorte, so their story seems of little immediate relevance.

That's also true of John Cariani and David Costabile, as Valetine's and Proteus's servants Speed and Launce. The characters' comic complaints are showstopping material, but Cariani and Costabile walk through their roles, expecting laughs that don't come naturally. Don Stephenson, as the strait-laced Thurio, and Paolo Montalban, as the self-important Eglamour, are better at making small characters into big audience-pleasers.

Magnifying miniature moments into major set pieces is a big part of how Two Gentlemen of Verona generates its appeal; of the score's nearly three dozen songs, many last no longer than a minute or two - they're musical musings that appear and vanish in a heartbeat. And as the numbers run the gamut of early 1970s-multicultural rock, you may feel as though you're being taken on a whirlwind tour of islands ranging from Jamaica to the West Indes to Manhattan.

This allows Marshall little leeway in establishing a directorial or choreographic language, as she could do in the more leisurely Wonderful Town; without time to develop her dances, they tend to look like scenes from a low-budget aerobics infomercial. Even her one moment of real inspiration, a Matrix-inspired battle scene (complete with ninjas) when Valentine and Proteus take on Eglamour, is less compelling than the dragon fight it replaces. Except in rare instances ("Night Letter" and "Bring All the Boys Back Home," a satirical jab at unnecessary conflict, engagingly sung by Mel Johnson Jr. as the warmongering Duke) when the movement closely derives from the songs, this production is more interesting to listen to than it is to watch.

That's partially due to the colorful but uninspired scaffolding set (Riccardo Hernández) and Elizabethan funk costumes (Martin Pakledinaz), and partially the pulsing musical direction of Kimberly Grigsby (who, on a bandstand high above the stage, is more viscerally eye-catching than most of what happens below), though her nine-piece band at times sounds perilously thin. And it's partially due to the score, which asserts itself as a Tony loser but pleases considerably whenever it's allowed to communicate youthful, exuberant energy.

Unfortunately, that's not allowed often enough. The frenetic, full-company finale, "Love Has Driven Me Sane," for example, is so staid, so self-contained, and so in keeping with the rest of the show you might wonder when everyone was supposedly insane in the first place. Except for the terrific Lewis and Goldsberry, this Two Gentlemen of Verona is nearly uninvolving enough to make you lose your own mind.

Two Gentlemen of Verona
Through September 11
Delacorte Theater in Central Park, Enter Central Park at 81st Street and Central Park West or 70th Street and Fifth Avenue
Pick up FREE tickets to Shakespeare in the Park on the day of the performance beginning at 1pm at The Delacorte Theater in Central Park, or from 1 to 3 pm at The Public Theater at 425 Lafayette Street, just south of Astor Place. For more information, please call 212.260.2400. Please note, there is a limit of 2 tickets per person.