With regards to Copenhagen I walked from the ship into the city centre as there are quite a few sites en route. For example, the little mermaid is quite close to the port and it seemed to be quicker to walk than wait for everyone to get onto the tour coach at the ship and then queue to get off it again a few minutes down the road! I have to say the mermaid was a bit of a disappointment but at least I saw it without a bus load of people gathered in front of it. From there I walked on past some very attractive buildings before reaching the main square and canal area where the main photos are taken. This all took around 30 minutes at a leisurely pace. A lot of the city is pedestrianised and if you walk through all of this you reach the Tivoli gardens. I recommend you get a decent guide book and map (and some comfortable shoes). There is also a shuttle bus service as already mentioned but with this you miss out on some sites on the way in, so maybe just catch it back at the end of the day.
Hi there. All of the ports that you mention are within fairly easy reach of the city centres and the couple that are a little longer like Tallinn and Copenhagen can be reached with the provided shuttle. I would suggest that you spend some time looking at the various "tourist" sections provided by the cities concerned, web sites like VirtualTourist etc and cruise critic and read reports and reviews that other tourists have made so that you can make a really good judgemental decisions as to what to see and where to go and what the pitfalls are. It will cut down your costs and give you a far better itinerary. I also use the various cruise excursion descriptions, not go on them but make sure that I am aware of their highlights and if I want to see them without being taken to a rug factory or pottery or papyrus selling point. Hope this helps..... Neil.