Haven't been there for Christmas, but we've been there for New Year's several times. The resort is much quieter than it is in the summer, even if it's at full capacity! The weather is cool -- we haven't had to wear heavy jackets, but definitely not shorts weather for us! There are always people in the heated pools, no matter what it's like outside!
The resort activities are basically the same as other times of the year, although they may not be offered as frequently as they are during the summer months.
I think it would make a great place to stop to unwind after WDW!