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We did a Greek Island Tour a few years ago with "Classic Journeys". Six in our group although they would have gone to 10. At 12-14, they would have considered splitting the group.

We spent three days in Athens, guided by new friends in a local Rotary Club we met the first day. Our discussions were a little English, some Greek from a CD and French. Drove to several "local spots", and eateries, and had a great local experience. Skipped the Acropolis, been there, done that.
Flew to Crete (Hania) where we met our guide and the rest of the group. Three and 1/2 days in Crete, what they called a "Cultural Walking Tour". More travel on foot although we were shadowed by our Mercedes mini-bus. Stopped in small villages, walked all over Knossus (Labyrinth), Minoan grave/caves 3000 years old, etc. Then a high speed ferry to Santorini, for another three days in a boutique hotel. We did all sorts of stuff. The cruise ships came in at noon, dropped anchor and off loaded busloads for 3-4 hours to an area of tourist shops and then bused them all back and left. We were so glad that we weren't on the ships or the buses.
If you like to cruise, the ships are set up for that. If you want to see Greece or Italy, IMHO, avoid the ships. I've spent time on Sicily, Malta, Crete, Santorini, Gibraltar and Mallorca. Looking at Monaco, Corsica and Sardinia next. Classic Journeys was 5 star all the way.