the thing about “must see” places is that they are all pretty touristic and everyone just sees them because they must.
Sure, the Colisseum in Rome is one of those places where you have to form a queue and pay a ticket, and take pictures next to some poor Pakistani immigrant dressed as a gladiator (what? you really thought those guys were Italians?). And of course there are amazing museums, but once again you have to squeeze in with all the other fat Americans trying to take pictures.
I guess it all depends on your own reasons for visiting the country. The Vatican for example is quite interesting, if only for the fact that it’s so tiny. And of course it would be even more interesting if you’re a catholic. I’d go to San Marino for a similar reason (plus you get lots of cheap stuff there due to the low taxes).
Venice is unique in that it is on water, and if your road takes you that way, it’s worth getting lost in. I find the whole gondola experience too cheesy and far too expensive myself, but some people may like that. Though try to avoid it in the summer – films don’t usually portray the smell of a city built on water.
I’d agree that Florence is the nicest city, though unfortunately most tourists seem to agree with that too. Never been to Etna, but that sounds interesting. And I’m not too keen on the south overall.
But there are amazing little corners in every country, and if you have the time you might want to get off the beaten track and perhaps take a bus ride to some suburb where everyday people live. There was this huge computer hardware store in some neighbourhood in southern Rome where all the people went to shop, and across the street there was this amazing restaurant with the best spaghetti in the world for about a quarter of the price it cost in the city centre. That’s where actual Italians go to eat. And there are nice mountains up north, and a beautiful lake near the Austrian border where you could actually swim in the summer. There’s a wonderful castle on a cliff on the west side, but I never figured out how to get there.
That sort of thing.