Judging from the comments on this site, New York seems to be a town of hard core sushi purists. Are there any modern Japanese restaurants, similar, for example, to Zuma in London?
Not true. London has some incredible Japanese restaurant. Check out Roka on Charlotte Street (Fitzrovia), Umu in Mayfair, and Chisou on Princes Street (Hanover Sq.). All three are up there with the best in the world (in my humble opinion).
a new restaurant in union square called 15 EAST has one of the best sushi chefs (masato shimizu from jewel bako) and a contemporary atmosphere. it's owned by the same people who did tocqueville, so the kitchen food has french/new-american twist.