I have done Christmas week @ Disney World 3 times, including the 1999 to 2000 millennial. For perspective, we also do mid March Spring break almost every year.
Christmas week, is just like spring break. yes, it is freaking crowded. but, with planning you can still do pretty much everything. just like spring break. Only the weather is a little more hit or miss.
the problem with Christmas "week" is you have 2 holidays in CHRISTMAS, and New Years Eve, where the parks are at capacity like thanks giving day, or the 4th of july. That throws things off a little.
If you have never done Disney at Christmas...I say do it. At least one time. But if you have already done it....reconsider.