It is an outstanding cruise. St. Petersburg is amazing. Tallinn, Estonia was the real sleeper, actually my favorite of all the ports.Copenhagen was great too.
Generally this is quite a port intensive itinerary with almost no days at sea. We embarked in Dover so that gave us a few days prior in London too. We rented a car in Germany and drove the autobahn, what a thrill! I cannot say enough good things about this cruise.
Helsinki was my least favorite port. It was a bit hohum.
I hope this helps.