Hi Marcus
Up until last year we'd visited mid-May to Mid-June in our previous trips. Went from 16 Oct to 1 Nov last year . . . and going back same time this year we loved it so much
We found the weather perhaps ever so slightly cooler than we were used to for the first few days (85 degrees instead of 90

), but then it hit the high 80s to low 90s and stayed that way, particularly when we went further down south.
We really did enjoy our trip in October and, like Kaylee says,
MNSSHP is a must. It was the only time we visited MK so we spent 7pm - midnight there (there I was thinking we'd probably only stay an hour or two . . . we had to be kicked out of the park on closing at midnight

). The rides - with the exception of Haunted Mansion - were ALL walk on. The Headless Horseman parade was great and when we finished watching that we went straight on Big Thunder Mountain Railroad and watched the fireworks while being chuntered around there - magic.
The crowds were smaller than we were used to in May, but perhaps because we stayed ovenight at HRH and got front of line access in both Universal parks made a HUGE difference.