Is fun. But is it ever slight! By contrast, the La Jolla Playhouse's Cry-Baby, an imitation John Waters piffle, seems Sophoclean. In a way, Xanadu beats a dead horse. It parodies one of the, if not the (say some), worst movies of all time: the 1980 Olivia Newton-John fiasco in which Clio, the Greek muse of history, abandons immortality for the chance to fall in love with Sonny, a Venice Beach chalk muralist, and create art - well, okay, build a roller-disco. What saves the musical, some, is that the playful parody forgives the errors of the original's ways. What also saves the show, for some: Douglas Carter Beane's book pays homage as much to the era of mirror balls and leg-warmers as it does the movie - and clearly envies their late-1970s naïveté. Beane's best lines, however, are in-jokes for theater cognoscenti that evoke intermittent bolts of laughter amid pockets of dead silence. The Christopher Ashley-directed cast performs with energy and does justice to the music - especially when Sharon Wilkins and Joanna Glushak belt "Evil Woman" (better justice, in fact, than the live band, which sounds synthesized). Max von Essen makes Sonny two different people: the near-brain-dead male ingenue has a mature, powerful singing voice. The show's star, Elizabeth Stanley, who played Allison in the Playhouse's Cry-Baby, warps Newton-John's Aw-zee accent (and gets laughs the first time, but not the next twelve) and deftly skates around designer David Gallo's restricted performing space. She handles "Strange Magic" and "Suddenly" with ease. She even sounds sincere when she croons the goofy ditty, not in the original, which asks THE metaphysical question of the disco era: "Have You Never Been Mellow?"