Traditionally, there are meet-and-greet opportunities with rare prince and princess couples (Philip and Aurora, Tiana and Naveen, etc.). There are also usually a few small decorations up around Town Square, but that area is currently walled off, so I have no idea what will happen with that.
It’s usually more crowded than the days around it, particularly in the afternoon/evening - a lot of couples seem to take the day off, or at least the afternoon off, to hit the parks.