I should preface this review by saying that even a bad cruise isn't totally bad. On the other hand, I haven't done a Carnival Cruise in a while (ha).
4 out of my last 5 cruises have been on Holland America but this Zaandam cruise was (by far) the worst.
My first cabin was 1882 on the Dolphin deck. On the first night of the cruise the seas became a bit rough and we began to hear this loud crashing noise as the ship rolled to starboard. Then 3 or 4 seconds later there would be another crash as the ship rolled back to port. Since the crashing noises always came in pairs, I have a hunch it was a heavy door opening and closing on the ship someplace. The guy in the cabin next to mine (1878) was going nuts by the second night. Others in that area of the ship were bothered by it too. The ship's crew would not tell us exactly what the problem was. They made plenty of suggestions but none of them made any sense. I am sure they knew exactly what the noise was because after many complaints, they finally gave us a different room.
See Comments above for cabins 1882 and 2542