As someone who goes that week before Christmas, I agree with many of the comments above. Crowds get worse as the week progresses, but still manageable.
One thing that works in your favor this coming year: Christmas falls on Tuesday and, unlike the past few years, many schools will not have the entire week (Dec 17 - 21) off before Christmas. Just a hunch, but I suspect it'll be a little less busy the beginning of that week than it has the past few years, with more noticeable shifts late week as schools start their winter breaks closer to Christmas.