Definately getting together and spending time with my family. Decorating the tree and the house are fun too, especially when shared with children. I also like the food. Which reminds me, it's time to start thinking about what I'll make this year.
I have to say that I'm not a big fan of Christmas, I don't particularly enjoy the commercialism of it, and the need to buy unnecessary things. However, I do like that Christmas brings family together, which can be a rare moment in otherwise busy lives. It's also lovely to see children get into the spirit of Christmas, and to see their joyful faces on Christmas day morning after Santa has visited.