Did you join a group for the tour, or were you just two.
Suggest you research this on the internet - lots of suggestions on ports of call section on site called cruise critic.
All bar St Petersburg can be visited independently if you do not want to go on an organised tour - there are shuttle buses from the ship but as Aldrich suggests you need to do your own research to prioritse what you do. Oslo is charming and you can walk into town, see the palace and come back via the waterfront and tour Akershus Castle, which is right next to the ship.The changing of the guards at both Copenhagen and Stockholm is good, as is the Vasa museum at the latter. Tallinn is a little gem just to walk around from the shuttle bus and St Petersburg is just mind blowing but do book tours either through the shio or privately. Also decide how energetic you want to be as nine hour days touring do not suit everybody. Options include a panoramic tour of the main sights, a canal
trip, a trip to the superb churches, to the Hermitage museum and to the royal palaces a few miles outside. You cannot do it justice in two days so choose what yoy want and what to leave out ... until next time.
Save a lot of money in St Petersburg by organising your own trip. We did last year and it was well worthwhile. we were recommended to Alla Tours. Contact Alla Ushakova at firstname.lastname@example.org She and all her staff speak perfect English. Ask for Angelika as a guide. She was lovely. They organise your visa etc. They have a choice of options tourwise. You can make up a party or as we did just two of us. Other passengers were amazed at how much we'd seen. You are met within feet through customs and really looked after. We were also given a 3 hour DVD of St Pete at the end of our trip.