First decide on your goals and what to see

I'm coming from the bias of enjoying cruises

Do you want to soak in the sun, experience life on many islands, or is this an attempt to see the tourist highlights? As others have noted, cruises offer the opportunity to "skim" life in a country and see the big attractions.

One of our most enjoyable cruises started in Barcelona and stopped in Monaco (meh), Florence, Rome, Naples (Pompeii, Capri, Amalfi), Mykonos, Athens , Kusadasi (e.g. Ephesus), Istanbul, and Venice. That covers 3 or 4 of the most important cities in history. Many cruises have stopped going to Turkey (political situation) and Venicce (local restrictions0, but substitute other stops.

In Athens we saw the Parthenon and the Museum. Mykonos is a nice beach stop with the patented white stone buildings with lunch in a local taberna.