I would not recommend Meditarrean cruise as that would definitely not enough time at each port - especially it takes long distance travel from port to sightseeing points. Med cruise also is very port-intensive - one would get very very tired after 3 or 4 days. (Med cruise usually is 10 to 12 days long).
OTOH, Baltic sea and Northern Europe is particularly well-suited for cruise - you only need to look at the map and see why.