Voted mediocre, because they're too map dependant. The more coastal cities/etc able to give food to Venice you get the better, the more places to trade with the better. Starting near an overglorified lake-sea is heavily crippling.
Also Venice can get less cities before they drag your science down. What I mean is puppets generate less science, and there's a science penalty per city... That means your cities will much slow your science down much faster. Even worse if you consider that Venice benefits a lot from Commerce's finisher, which means Rationalism may not be taken till much later.
Also painful to see beatiful land with NW/great tiles you can't take, because you have no Settlers, and AI is usually too stupid to settle a city in the proper, perfect spot.