Our Baltic cruise stopped at Warnemunde. We took the ship's excursion to Rostock and I agree with Susan that it was just ok. Their was a street fair on the day we toured which made it more fun.
I did enjoy walking around Warnemunde, visiting the shops and just "looking". If I had to do it over again, I would forget Rostock and spend all my time in Warnemunde.
And, Anaclaire, we didn't want to do an 11hr excursion to Berlin either. Turned out that we made the right choice as the bus was involved in a traffic accident in Berlin...no injuries but delayed the return to the ship and 11hrs turned into even longer!
Enjoy your trip.