Next year could be different, this year was the first year they formalized Halloween celebrations and advertised which sailings Halloween would be celebrated on. I know
DCL will have gotten lots of feedback from guests on what they liked and didn't like. I'm hoping they will expand what they had on the Dream to all of the ships.
Personally I was disappointed in the Halloween celebration on the Fantasy. I really wanted to take DD trick or treating but they didn't have that, we didn't even get a bag of candy in our stateroom. At least she is too little to know what she missed. I did like the photo ops with the characters in their Halloween costumes.
I thought that trick or treating was advertised as part of the celebration but I could be wrong.