For me personally, cities or places I can’t fly/get to easily. So I did a Baltic in 2017 on NCL that included an overnight in St Petersburg, and last year I did the Norwegian Fjords cruise. Those are my only two Europe cruises I’ve done if you don’t include the U.K. staycations which went nowhere.
I’d actually visited several of the ports on the Baltic cruise previously, but the main aim of that cruise was SPB. On that Baltic cruise, I had a great time in Rostock and Warnemunde (the ‘Berlin’ port) and Nynashamn (the ‘Stockholm’ port) and they are both places I never would have visited myself but were great.
I’d never visited any of the spots on the fjords cruise but I’d previously been to Oslo.
I would also prefer they did multiple fjords cruises (and at least one not in school holidays, and therefore reasonably priced!) as it’s one of the most popular itineraries.
I’d also like a 7 night France/Spain cruise, maybe hitting La Rochelle, Bilbao, and a couple of other spots.
Basically I don’t want to see a large city I’ve likely already visited, unless it’s somewhere like SPB where it’s much easier on a cruise vs flying there (obviously I do not mean visiting now.) Going to Rome, Barcelona or Athens hold no interest to me on a cruise.
I would also not object to a Greek island cruise or maybe somewhere like Sicily but not at the price Disney wants for them.