We were there over the 4th of July this past summer. I was hesitant to go during that time because I was afraid of the crowds. Well, we LOVED it! The special fireworks displays were amazing. It was crowded, but still very manageable with good planning. We were always there when the parks opened and then went back to the room to swim and rest during the afternoon heat. I loved the long park hours.
We have been the first part of June, the middle of June, the week after Thanksgiving, the second week in December, and 4th of July. As awesome as the Christmas decorations and events are, I still much prefer summer because of the longer hours.