It's not a bargain if you don't enjoy the show. We asked The Post's drama critic, Peter Marks, which new plays have the theater world buzzing. His picks:

* "Sweeney Todd, the Demon Barber of Fleet Street." The latest revival of Stephen Sondheim's musical about a homicidal Victorian barber with a sharp set of grievances -- and even sharper set of razors -- trims the 1979 show to 10 actors, who not only sing but play all the instruments as well. John Doyle's stark production may be best appreciated by the Sondheim-obsessed, but there are thrills here for the uninitiated as well. Eugene O'Neill Theatre, 230 W. 49th St.

* "Jersey Boys." The music of the Four Seasons is the latest by a pop group of yore to arrive in the land of the show tune. Unlike some other recent jukebox musicals, like those adapted from the songbooks of John Lennon and the Beach Boys, this production, directed by Des McAnuff ("The Who's Tommy") actually got good reviews. August Wilson Theatre, 245 W. 52nd St.

* "The Color Purple." Adding Oprah Winfrey's name (and bankroll) to this musical adaptation of Alice Walker's popular novel has given the show spectacular mojo. But will fans flock to it if she's only the producer? We'll see. Even those who come away displeased will no doubt be happy to tell friends they'd secured tickets. In previews; opens next month at the Broadway Theatre, 1681 Broadway.

* "A Touch of the Poet." Serious plays have been flowing for years over to the houses off-Broadway, but a few large nonprofit theaters that operate on Broadway are managing to keep a spigot open. Roundabout Theatre is doing so this season with, among other things, this Eugene O'Neill classic. Gabriel Byrne, Tony-nominated in 2000 for "A Moon for the Misbegotten," is the star. In previews; opens next month at Studio 54, 254 W. 54th St.

* "The Pajama Game." Harry Connick Jr. is one of the bigger names to make an appearance on the legit stage this season, in a revival of a sprightly 1954 musical about labor talks at a pajama factory. (Other major actors will follow, including Julia Roberts, in Richard Greenberg's yuppie drama, "Three Days of Rain.") We know Connick can sing, but is he a song-and-dance man? You be the judge! Opens in February at American Airlines Theatre, 227 W. 42nd St.

Patti LuPone on the opening night of "Sweeney Todd."