We just did a mom and son trip from Dec. 16 - Dec. 21, 2016. We also did Dec. 25 - Dec. 30, 2015 and, in comparison, going earlier made a big difference in crowd levels. MK was always the most crowded and wait times build considerably throughout the day, so, if you plan to go to the parks early and make good use of FP+, it's definitely manageable. We really didn't find AK, EP or DHS to be too terribly crowded. Certainly the more popular rides, again, had longer wait times later in the day, but it was never wall-to-wall people like it was over Christmas week. The weather both years was in the 70's-80's (with lower temps earlier in the morning) and we could swim and wore shorts the whole time, but weather can be variable.