I generally hate cruises, but loved this one. Go.

We started and ended in Rome, and added days in Rome at the beginning and Orvieto at the end to get the "immersion" experience you don't get on the boat.

For Greece, we visited Athens, Santorini, Mykonos, and Rhodes. We also got to visit Naples (Pompeii), Sicily, and Ephesus (Turkey). We arranged for some private tours that were not run by the cruise company (Athens, Sicily, Ephesus), and did things like Pompeii on our own (just train tickets and site tickets).

There is no way we could have managed all than self-catering over land (particularly with a family of five). We are generally self-guided (currently on a Barcelona/San Sebastian/Bordeaux trip), but highly, highly recommend the Mediterranean cruise we did as the exception to the rule.

Enjoy.