We have been to Disney the last three Octobers and have really enjoyed it. The Halloween party is so much fun...we actually did TWO this last trip. October weather can be fairly hot. Not summer hot, but hot enough that a dip in the pool feels good. But the weather can also vary. We've had days of 90+ when we wanted to die (2012) and days of jeans and sweatshirts (2011). So it's really hit or miss.
Crowds are moderate. They're not low, and if you go to the MK on a non-party day, the crowds feel more like July than October. More and more schools are allowing for fall breaks and you can definitely see that with the crowds. Don't go expecting to walk on to everything...there will be moderate waits for most things. F&W turns Epcot into a zoo...an adult-themed zoo. We had some good luck with Epcot crowds this past year, but in the years prior the park was packed.
Overall, it is a good time to go. The weather is moderate, crowds are moderate, there is F&W, and the Halloween party, which is the #1 reason to go. We're doing our 2014 trip in December this year, and I think we're all a little sad about missing the Halloween party.