Cruising in the Med any time of the year is great. While it may be a bit chilly to enjoy an outdoor pool that is not heated, that will be more than offset by the fact that you will enjoy Europe during the shoulder season. We have been to Europe a number of times in November and December and love not having to wait on any lines. The weather while not hot is still pleasant. You probably don't even need to go on any excursions - you can do it all yourself.
By the way, another way to get around the Med is by ferry. We have taken the ferry from Italy to Greece, and traveled throughout Greek Islands, Turkey, Israel and a few hour layover in Cyprus. We did this during a three month trip of the area.