We were there 12/28/2013 - 1/4/2014. It took some planning but we had a great trip.
I tried to work in stuff outside of the parks like I said earlier - going around to the deluxe resorts to see their decorations one morning, hanging out at our resort, taking advantage of resort dining, scheduling a wine tasting at Jiko, etc. Fastpass+ was really helpful too.
As others have said, definitely bring layers. In looking at pictures from that trip we're in jeans and sweatshirts/long-sleeved shirts in the evenings, but earlier in the day we're in shorts and short-sleeved shirts. The weather felt great to us but we're from Ohio, sooo...
Have your ADRs and FP+ ready to go.
I know Epcot has "storytellers" around the World Showcase - I believe it's in each country (we didn't get a chance to do this but I have heard about it) and they talk about what the holiday traditions are for their country. In the Studios Osborne Lights will be going, like someone else said, as will the Christmas parade and Holiday Wishes at Magic Kingdom. With the removal of the Jammin' Jungle Parade and Camp Minnie Mickey from Animal Kingdom I am not totally sure what will be at that park in terms of holiday stuff...don't miss the tree out front though (would be tough to as it's huge) - it's my favorite park tree.
Congrats on your upcoming graduation!