Others have given you some good links. We went on the 11-night Med cruise in 2007. One of the things we did that really affected us having a great time is that I joined a thread with other DISers going on the same cruise. We became friends on that cruise, and several of us banded together to go on private tours, as opposed to going on Disney excursions.
We were able to tailor our tours to do the things WE wanted to see, and they were wonderful. There were usually 10-12 people on each of our tours (3-4 families on each & we split the cost of the tour among us).
Our highlights (my kids were 18 & 19 at the time) were our visit to Pompeii, and our visit to Rome (Vatican, Vatican Museum, Sistine Chapel, Coloseum-inside, Pantheon-inside, Trevi Fountain, & Spanish Steps). We enjoyed everything we did. Florence was too crowded, and we did go on a Disney excursion. Now I wish we had gone on a private tour with other DISers. We did take the Disney excursion to Monaco/Monte Carlo, and I really enjoyed that, so that one was good.
Have a great time no matter what you do.