A friend and his wife did just that last year - the ship is NOT the type of cruiseships we are talking about here, and the foods are far from the standard Fruit is looking for. The scenery is beautiful, but is also boring, after 2 to 3 days looking at Fjords and Waterfalls ... The cabins are also nothing to write home about, virtually no entainment. In short, this is NOT the resort-style cruiseships most people think of.
See my post about the possible choices for European cruises.
Actually most European cruises are very port intensive - literally everyday is a port day (not in the ocean, unless you are doing Trans Atlantic) - the problem though, is the port is far away from city center, such as, for Paris, the ship docks at Le Harve, and there is about 2 hours train ride if I remember it correctly - Le Harve to Gare St Lazzare in Paris. I simply dont see HOW people can enjoy the cities on an European cruise if their aim is to visit the cities.
The exception is the Baltic and Northern Europe cruise, Greece and Turkey cruise.
Baltic cruise usually docks at St.Peter*****urg for 2 nights - basically use the ship as a hotel for 2 full days of sightseeing at St.Peter*****urg.