You have heard, perhaps, that Madonna is a disappointment onstage and a pain offstage in her much hyped London theater debut. But never mind those snarky critics: the Material Girl is surprisingly engaging in this not-bad comedy about a New York City art dealer who ramps up a bidding war over a Jackson Pollock painting to save her fortune and her marriage. If Madonna's voice, oddly, is a little underpowered, her body is in fine trim; she slithers and writhes and pounces around the stage, giving us a teaser for her next concert tour while creating a convincing portrait of a woman forced to take desperate measures to avoid financial ruin. Oh, and there's some kinky onstage sex. I told you it wasn't a disappointment.