We've gone in October many times. We love it!
I think October is becoming a popular month to visit and while it's not crowded like a summer or holiday month it can getting pretty busy. We've been in September and I have to say that was the best time to go crowd-wise. But, it's peak hurricane season so you have to consider that.
As for the weather, for most of our October trips it's been really nice. It was chilly in the morning and evening but the days warmed up nicely. Little to no rain and lots of sunshine. I will say during on trip last October we never did make it to Blizzard Beach or spent much time at the resort pool because it was downright cold! We had to buy warmer clothes.
Debbie