The stage version of the 1958 MGM movie musical "Gigi" is a good example of what the late composer Mary Rodgers called a "why musical" -- a tolerable but ultimately pointless adaptation that adds little to, and is inferior than, the source upon which it is based.

"Gigi" is so identified with the actors from the film (including Leslie Caron, Maurice Chevalier and Louis Jourdan) and Vincente Minnelli's evocative visuals that a live adaptation is bound to be disappointing.

But more than that, its slight romantic plot about the courtship of a young girl in fashionable turn-of-the-century Paris does not provide the backbone to support a drawn-out stage adaptation.

And though the songs from the film are tender and pleasant, it's hardly "My Fair Lady" or "Camelot" (also written by Lerner & Loewe).

It originally came to Broadway in 1973 and flopped -- so the fact that anyone would give it a lavish revival is just bewildering.

The new production uses a revised book which mirrors the film's story but cleans up some aspects that now appear somewhat creepy -- like the jolly old man (played by Chevalier in the film) singing "Thank Heaven for Little Girls." Efforts to flesh out Gigi and her beau Gaston come off as labored.

Vanessa Hudgens, who shot to fame nearly a decade ago as the female lead of "High School Musical," plays Gigi. She is joined by a very capable cast of musical theater pros including Victoria Clark, Howard McGillin and Dee Hoty.

As directed by Eric Schaeffer ("Newsies"), the production has an elegant look and lively movement but nevertheless feels empty and stalled.

Hudgens gives the sort of sincere but clumsy performance you'd expect to see in, well, a high school musical. But all things considered, she has been given a near-impossible task of injecting life and charm into what is essentially a two-and-a-half-hour slog.

If you go: "Gigi" plays an open run at the Neil Simon Theatre. 250 W. 52nd St., GigionBroadway.com.