I've been at least 5 times and I've either had horrible weather and the sewers overflowed into the squares or was surrounded by such awful tourists at a scale I could not move through the narrow streets without feeling like other people's BO was getting rubbed on me.

There was one time where things were a bit calmer, but I only had 36 hours between spots. Made some good memories where I dared my kids to eat more gelato than I could, but the rule was you could not get more than one scoop at a single shop. A fun way to explore all of the little alleys and passageways.