We were there twice last October. In early Oct. it is still very warm and very humid - something we are not at all used to, so it was an issue for us. However, when we returned about the 19th, we noticed an improvement. It was still warm, but not as humid, and I thought the crowds were even a bit lighter.
One thing I was a bit surprised by was the off season hours. I always looked forward to being in MK at night. During off season, they do close the parks about 9:00 and Spectromagic only runs twice a week. Just so you know!
Good luck!