LEL knows a lot about sushi.
I wouldn'say I know alot, but I know some.
Nigiri-Sushi, with raw fish, is best left to a sushi chef. Buying raw fish is more complicated than just finding fresh fish; The taste varies with the cut, just like regular meat.
Hoso/Foto/Ura-maki can be made delicious with precooked crab,smoked salmon, canned tuna, fried salmon or salad shrimp; Also avacado, cucumber, carrot, shitake mushrooms, pumpkin slices(kampyo), pickled ginger, lettuce...There are so many combinations, and you don't even have use fish. Almost any vegetable or condiment you like can be used; cream cheese is very popular, also mayonnaise. I prefer brown rice to white rice, as it spreads easier and holds the vinegar taste a little better. If you boil three Arbol chili peppers and a clove of garlic with the rice, it makes it nice and savory. The seaweed, nori, is chock full of antioxidants, fiber, protein, etc. Very good for you.