We were on the Dream last year. They had all the restaurants decorated with large carved pumpkins which were cool and TONS of candy as you entered the eating areas. There were a few decorations elsewhere on the ship. They had a party that afternoon (I believe it was around 4) and because of rain, it was held inside at the bottom of the main staircase. All the characters were in costume and danced. They later had a costume contest (which we did not attend). That was about it. We went to the room later in the evening and there was a bag with candy in it for our DS. (I believe this was left at turn down service). There were a LOT of adults dressed up. It was pretty cool and people were really creative.
Have a great time. I'm certainly glad we experienced it.