Since you're writing from London, I assume you haven't seen the show in Brooklyn, so the first thing I'm wondering is how you can dismiss an exhibition that you haven't even seen. Consider yourself a member of the Rudy Giuliani School of Art Criticism--the mayor, too, has not seen the show.
I have been out to Brooklyn several times to see "Sensation," and I think it's a wonderfully spirited show. Obviously, not every piece in it is a masterwork, and there are more than a few dogs. But, on the whole, I felt moved by the level of energy and feel that the show provides a welcome antidote to the New York scene, which at the moment is suffering from a severe case of theory-itis. "Sensation," to its credit, isn't about Derrida or Baudrillard or gender-bending or the reified moment of perception. It isn't about political correctness. Generally speaking, it takes art away from the theory people, from the academics with their 10-pound books and their unbearable jargon, and allows real life to come shining through.
Take, for instance, Damien Hirst's shark piece. It occupies a giant glass box and so obviously harks back to the geometric forms of the Minimalist movement of the '70s. Yet it's also a critique of American Minimalism, which at a certain point became too elegant and mannered for its own good. Minimalism, in the end, became an art of polished, quite exquisite surfaces--and Hirst wants to get us below the surface, into a deep, muddy ocean of feeling. Hence, the shark, the perfect below-the-surface symbol. At any rate, I love the shark piece. Maybe I'm just a sucker for icons.
By the way, I think it needs to be said that Damien Hirst isn't nearly as dangerous as Mayor Giuliani. Damien Hirst is not running for the U.S. Senate.
As to Chris Ofili of Holy Virgin Mary fame, I think he's a solid painter. Ofili is a black Roman Catholic, and to my mind the picture represents an earnest attempt to appropriate the Virgin for black culture. I have no problem with elephant dung (which is just chewed up grass anyway), and I'd guess the reason the painting set off such a furor is that it depicts a black Virgin Mary. I think Giuliani freaked out when he saw a Virgin Mary who wasn't white. I mean, it's probably not a coincidence that the mayor decided to single out (and all but lynch) the most prominent black artist of his generation. That's a shame, especially since the Brooklyn Museum of Art is the only major art museum in New York that serves a racially diverse community.