This year we visited in mid-November and last year the first week of December. The weather was exceptional for both trips no rain, sunny every day, highs in the upper 70s to about 80. Slightly cold, IMO, for swimming when it was breezy. Crowds were about the same as summer and spring. Honestly, crowds always seem about the same to me. By December all the Christmas decorations are up but they weren't fully up at the Grand Floridian by the day we left this time (Nov 19). The Christmas party starts in early November. The parks, particularly Hollywood Studios, looked fully decorated. I love that time of year and would definitely go again! It's nice to be comfortable walking around all day!