Take it from a guy who lived in Japan, married into a Japanese family, and had a full-course, Japanese New Year's dinner yesterday.......Sushi on Tropicana is the bomb.
They specialize in exotic rolls, nigiri sushi, and a full Japanese menu for folks that don't do the fish thing. They have plenty of good cold beer, sake and plum wine too. It is about 2 miles east of the Strip on Tropicana.
All you can eat for about $30/person. Everybody that I have taken there returns for more.
If you can't make the Trop location, the also have Sushi on Rainbow.