Step Up 3D isn't, in dramatic terms, a very good movie, but it's the first film in a while to use 3-D as more than a marketing ploy; it points toward an original way of making a musical. The dance sequences are glittery, percussive explosions of citified youth energy. They feature a lot of break-dance moves that are 25 years old, only executed with a stomping new aggression, and the 3-D lends them a stroboscopic, almost vibratory aura. The in-your-face visual flash is exciting. It helps to compensate for the film's hyper-thin plot and faux ''street'' corniness, with teams of dancers facing off in competitions that turn them into gangbangers gone Broadway.
The heroes are the Pirates, a rainbow coalition of hoofers who, in a sense, are the perfect image of racial and sexual integration: They're all equally bland. Except, that is, for Moose a moptopped, floppy-limbed teen upstart played by Adam G. Sevani, who looks like Michael Cera impersonating Maya Rudolph and who dances like a marionette on helium. The editing is chop-chop manic (as if the 3-D weren't grabby enough), but then Moose and the girl he likes (Alyson Stoner) do a sidewalk duet in an unbroken two-minute take. If there's a third Step Up sequel, it would do well to let all these kids spin and pop in their own space and time. B-