We have been going to WDW for Thanksgiving for the past 15 years. It has become much more crowded lately, but that is a relative comparison .
Lately Thanksgiving crowds are a 10 out of 10 from Tuesday - Saturday. Everyone's opinion is based on their experience and if you are a first timer you need to be prepared. You must have dining reservations for the popular places. You must have FP for the popular rides and usually only in MK you will be able to get 4 FP for some of the "good rides". QS will be crowded with queues for the lines at popular times up to an hour, and TS walk ins will be non-existent for most of the popular restaurants. We have seen waits for It's a Small World at 45 minutes, HM at 120 minutes, Soarin 240, FoP 300.
We were forced into going this week due to schedules in the beginning and have grown to love it. BUT it is not a week for the faint of heart IMO. It is busy and patience is a must. Just my opinion.