I don't think it's so much that people are let down after Christmas and they are disappointed that Christmas doesn't meet their expectations. Uncle Joe gets in a big argument with Aunt Beth, the kids are constantly fighting with each other, and now you have to face all those bills.
Keep your expectations low, your gifts simple and just go with the flow and things usually work out much better.
And also, it helps to remmember that all that crap, gifts, parties, etc. have absolutely nothing to do with the celebration of Christmas.
The true light that gives light to everyone was coming into the world. He was in the world, and though the world was made through him, the world did not recognize him. He came to that which was his own, but his own did not receive him. Yet to all who did receive him, to those who believed in his name, he gave the right to become children of God— children born not of natural descent, nor of human decision or a husband’s will, but born of God. The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the one and only Son, who came from the Father, full of grace and truth.