Whenever I am in Boston, I always make a point to visit Aji for at least one meal. I often bring friends or colleagues with me, and everyone has always had high praise for the food.
The fish is cut into good-sized portions; the preparation and presentation is fantastic; and the wide variety of interesting (and tasty!) house rolls will give you lots of experimentation over many visits!
They also have a decent variety of sake and other beverages.