Since you don't say if you have the money to rent a hall or not, if you do not the open house idea would make the most sense. A friend of mine did one for Christmas. They had the gift exchange which was set for a specific time. But for us that did not want to participate in it, I was able to come early, talk and meet some new people and leave after a couple of hours. They had people coming and going constantly from 2 pm to 8 pm. They got to spend time with all their guests and everyone had a wonderful time.