We went Thanksgiving week of last year. I researched crowd calendars and picked our parks based on those. We are rope droppers, also, FWIW. We had a great trip. We honestly didn't notice the crowds being worse than any other time of year, but again ....
best parks and rope drop. I think those things are key.
Had we gone to the most crowded parks each day at the most crowded times, we would likely have had a different experience.
http://www.easywdw.com/category/calendar/11-november-2015-crowd-calendar/
I'm not sure what you mean by "transformation". We didn't see anything like this. Christmas decorations were already up except for the tree at MK. Other than Osborne Lights at DHS (which were mind-blowing), I was pretty underwhelmed by the decorations. They were nice, but just not the WOW I had created in my mind. We did enjoy the gingerbread display at the Contemporary and some of the chocolate displays at the BC/YC. The tree at AKL was pretty. But again, just nice. I guess I had blown this up in my mind to be a bigger deal that it was. A case of expectations getting in the way.
FWIW - we took it easy on Thanksgiving day, slept in, late breakfast at Boma, and dinner at Hollywood Brown Derby that night - Osborne Lights after. It was a festive way to celebrate the day, and DHS was a "best park" and not gridlocked.
I wouldn't hesitate to go back that week. Other than rain, we loved the weather.