IF you're "lucky" enough to get in before capacity, it's absolute mayhem and insanity. You cannot / will not ride anything, you're literally touching a stranger at all times (this may or may not be a bad thing, depending on your personality), and prepare for 20 minute line up's just for the women's restroom (any restroom).
I suppose it's a subjective thing, but xmas day was just waaaay too crowded for our tastes. Unless you're there well before noon, you likely simply won't get in, as most of the parks stop admitting before noon, due to capacity.
We like going to DtD - much less crowded, and we still get a disney fix.
I feel bad for the families who come down on their "once in a lifetime" family disney vacation, and think it will only be more magical during the holidays. It's unspeakably crowded, chaotic, and rushed. Sorry, don't mean to paint a poor picture for you. If you have a large tolerance for crowds, serious crowds, you'll be okay.