Sushi Nobu is very, very good.
Social House at TI is very good as well.
Shibuya at the MGM has great sushi as well.
Part of it also depends on what it is you like.. if you are a sushi, California roll lover, middle of the road is fine. If you like the more exotics.. the sashimi, octopus, quail eggs... you want to go to better places.