We took the city bus (a 5 minute walk from the ship) to the old town (Pile Gate), went to see the multi-media city history overview just inside the Pile Gate, then bought tickets and walked half-way around the old walls. We walked down to the old port, had some gelato (yum!) and then took a 15 Euro, 45 minute boat tour. We walked some more in the old town, then took the city bus back to the ship.
Herculaneum was a 5, but the tour guide a 2--we couldn't hear him, the crowd was too big, and his English was difficult to understand. It was also VERY hot. We've done Pompeii and Amalfi Coast before--both outstanding trips.
Bought ticket at Corer Museum on St Mark's square (interesting, not crowded), then skipped long, long line for Doge's Palace. Self tour at Doge's - there are signs in English explaining each of the rooms. Lots of history, architecture, and art.
Murano Island Rating:
Caught a tour given by one of the glass houses - 15 Euro pp for round trip private water taxi ride, tour, glassblowing demo, and tour of their numerous showrooms.
St. Mark's Square Rating:
Had a 24 Euro! Bellini on the square at a historic cafe, listing to chamber music and people-watching.