We went here not once, but twice during our week in Venice. It is simply the best seafood restaurant around, and it is definitely not the most expensive. We tried it based on other TripAdvisor reviews and fell in love with the food, service, and atmosphere. The first time we were a little nervous because it looks from the outside like a hole in the wall, but once we came inside and were welcomed and seated by the aquarium (which the waiter later took the time to point out all the fish and other animals in the tank to my two children) the evening just got better from there. I would recommend the fish tacos and the shrimp was excellent as well.
Word of caution: I saw signs that said they were closed from 2-4pm to prepare for dinner, so don't come then!