My wife and I took this cruise with her parents who are both in their late 70s.
This would be their first sea cruise but they have done many river cruises before.
The Arcadia was first rate. Apart from the occasional dodgy evening entertainment everything about this ship and her staff was first class. The food was amazing, the service incredible. The cabin maid worked her socks off as did all the cleaning staff. Playing cricket as we crossed the North sea was a pretty unusual experience. The seas were very kind with every day a millpond.
We stopped in Oslo, Copenhagen, Stockholm, Helsinki, St Petersburg (2 days), Tallinn, Warnemunde and finally Gothenburg. In all the ports except St Petersburg we just made our way into town and looked around. In St Petersburg we used a local tour company for a 'relaxed' private tour.
The only port that I would not return to would be Copenhagen, a bit like Birmingham but with less charm! Everywhere else was very pleasant. Tallinn in particular was very charming if a little crowded.