I did MK the 26th (and DAH), AK the 27th (prior to the party), Epcot the 28th, DHS the 29th and MK the 30th.
MK on the 26th was crazy but I was expecting that because it was only 1 of 2 non party nights. I was doing After Hours so it got A LOT better during that.
AK the 27th was manageable except for Pandora. It was so crowded you could barely move it was very underwhelming. The Safari was backed up too, I had a FP and still waited 30 minutes in line. Expedition Everest is my new favorite attraction in all the parks. Single rider line I waited 2 minutes each time. I rode it 4 times in a row.
Epcot was good except for parts of World Showcase that got jammed up.
DHS was a massive letdown. Park was so crowded it was difficult to move around and Toy Story Land was miserable. They also cancelled Fantasmic due to technical difficulties so that didn't help with my impression of the park overall.
I'm glad I got to go at Christmas to see all of the beautiful trees/decorations but I would never go this time of year again.