It is true that Mr. Ai includes personal, social and political references in his sculptures. At times they can seem like the coded messages of a prisoner tapping on his cell wall. "Surveillance Camera" (2010), a marble sculpture that turns an object of oppression into a work of art, is ominous and poignant. But often the sculpture, outsourced to inexpensive Chinese artisans, is a lot of effort for not much return. Sculptures that require lengthy explanations—that one was inspired by a small wooden box left by the artist's dissident poet father, Ai Qing, or that one was inspired by the shaking of the chandelier in Sergei Eisenstein's 1928 film "October"—are not so much "warm" as warmed over. One exception is "Straight" (2008-2012), a new floor installation made up of 38 tons of rebar recovered from Sichuan after the earthquake that is a rough and powerful work regardless of what else we know about it.