Well, each year it gets more crowded. This year will probably be worse with
free dining available. Here's the thing, last year we went the first week of December instead, which traditionally is the slowest week of the year, but I found it to be just as crowded if not more than Thanksgiving week.
Plan to wait in lines. Parades, etc. will be packed so get your spot early. Dining reservations are a must, there won't be any walk-in availability. The way I look at it, the parks are always crowded anymore. Unless you go during an undesirable weather season, you'll have crowds. Having it in your head that there will be crowds, using a good planning strategy, and just not letting things get to you is the best advice I can give.