J.M.W. Turner (Metropolitan Museum, up through Sept. 21). The Met’s 140-piece Turner retrospective, the first full-scale look at Turner’s work ever to be mounted in America, is a once-in-a-lifetime occasion, a priceless opportunity to track the evolution of the nineteenth-century English painter whose late canvases (generously represented in this show) march right up to the very brink of abstraction. Like most blockbuster shows, this one is far too much of a muchness, but if you can stand in front of a painting like this without being thrilled to the marrow, you’re looking in the wrong direction (TT).