We went on the Maasdam last year. Will you be visiting Visby? Great Swedish port. We started in Stockholm so did not take shore excursions there. We did visit Helsinki and I'd advise against the city tour. My husband says that everthing you need to see here is in walking distance of the port except the Rock Church. Senate Square and Market Square are the main areas of interest. There is Sibelius Park named for the composer with an impressive sculpture, but certainly not worth the bus tour.
Feel free to e-mail me, but put in the subject box shore excursions so that I open the e-mail.