We just returned from 12 days on the Carnival Splendor. We were on the first sailing of the Splendor to Northern Europe. Overall the ship and the ports are fun and interesting.
We spent a couple of days in London and left from the Victoria bus station. For those folks using the Carnival transfer from the Victoria station to Dover make sure that you are at the right Victoria station as there are three. You want the Victoria COACH station--it is not part of the train station. The departure from the coach station was a mess.. too few Carnival staff and too many cruisers. There is essentially no where to sit or stand so be patient.
Arrival at Dover after a two hour ride was without incident and getting on board was quick and smooth. The ship is of course interesting and very, very pink. The designer clearly loved the color pink as it is everywhere. The ship's crew were to a person lovely, courteous, and helpful. We were disappointed that the cruise director was "John" as we were on an earlier cruise with him. He will take a 2 minute announcement and stretch it into an hour. He loves to hear himself talk.
Everything was on time and on schedule. You spend a couple of days at sea and that is nice just to relax. The schedule after that is very hectic.
The only place that we took a Carnival tour was in St. Petersburg, Russia (and you have to if you want to get off the ship). Every other port is very easy to do on your own. We had a blast taking the local transportation--train, subway, barge, you name it we did it. We walked and walked every port and had a wonderful time. Look online for walking tours conducted by locals as those are more fun than the Carnival tours. In Copenhagen we found a great one that left from a local coffee shop and it was perfect. If you choose not to go to Berlin my suggestion is get off the ship and walk 100 yards to the ferry that goes to Romstock. It is a one hour ferry and then take the train back as it stops right at the ship and runs every 15 minutes. Romstock is beautiful!
All in all it was a fun and informative trip that Carnival handled beautifully. One note of caution--the ship's laundry is a mess. We sent clothing a couple of times and both times they lost items that were never found.