As a kid I loved the anticipation of what might be under the tree, tip toeing down the stairs to do a bit of recon before creeping back up, avoiding the third step and it's telltale squeak.
Waiting for my siblings to stir, getting the dog riled up so they woke up whether they wanted to or not.
Going into my parents room and gently trying to get my Dad to wake up, slowly trying to pull his eyelids up to see if he is awake, (warn 5 year old fingers usually would wake him up).
Once he was awake, we had to wait for what seemed like months while Mom made coffee and Dad lumbered around filling the stockings and drinking the Brandy we left out for Santa (Dad said he was lactose intolerant and the brandy helped settle his stomach from all the cookies). When everything was ready, we had to let my little sister descend the staircase first since we had run her over in years past, going through the packages like Rosie O'Donnell at a buffet. Those were my favorite memories of Christmas.
Now my favorite part of Christmas now is giving to my kids and friends, seeing the joy of little ones as they unwrap gifts is awesome. The downside is the commercialism that crowds out Thanksgiving and turns Late October through December into a selling season.