i am a past halloween disney cruiseline passenger. you will find all of the kids club staff in costume (when we sailed 102 dalmations had just come out so there were dalmations running amok in the kids club), there is trick or treating on deck (not great-same treat at each station, we ended up preplanning a trick or treat from cabin to cabin for those of us from dis boards which the kids enjoyed much more), a costume parade and contest for kids and adults (and people go way out-our favs. were a family of 4 that did cinderella, prince charming and mom and dad as the ugly stepsisters-dad's mustasche made the outfit), loads of people with decorated doors and cabins (some brought battery powered lights for their verandahs) and lots of people who LOOOOOOOOOOOOOOOVE HALLOWEEN!
a couple of tips though-take light weight cool costumes (the common areas get very crowded and warm on halloween night) and have your camera at the ready-the characters were also in costumes!