European cruises are not your good choices, Except one or two

Baltic and Northern Europe

Greece and Turkey

These may be the only 2 that are good to use cruises, as the geographic set up works - i.e. the cities are right next to the ports where the ships dock.

Med cruises - there are several variations of such
is generally NOT a good way to do because the city center is very very far from the port - it usually requires an hour to 2 hours train or bus ride to get into city... enough said.

So, the key is WHICH part(s) of Europe you want to see, largely determine whether cruise is a good choice.

It cannot be generalized.