We were on a Fantasy Halloween cruise over Halloween itself this past year. Similar to you, it was just a fluke date thing, rather than us being drawn to a Halloween cruise. We aren't big Halloween people, either, and didn't find it to be overwhelming on the ship. There were some decorations around the ship, and certainly activities around it, but we didn't really go to any of those other than trick-or-treating. We didn't feel like the Halloween activities, as people who weren't interested in them, were a negative to our cruise experience overall.