The thing is if you have never been during other 'seasons' it is hard to find the value 'slowest' season being...what one would think..like empty. That is not the case. This is Disney after all

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I have been twice during Memorial Day week...and that is very crowded to me. When POTC has a 30 min wait time...That is crowded!! lol.
Yet when I go in the Value seasons, once in Sept, first week of Dec, and last part of Feb/early March, the crowds were a bit lower, except during the Dec one, but that mainly was due to MK, and ABC prerecording of the Christmas Parade. As soon as I walked into MK, saw what was going on, and the crowds, I left and went to MGM...lol.
Now when I went in Sept, this was 2004, after 2 hurricanes had gone thru, and another threating, so the crowds were low. When I can go on BTMR 3 times in a row with no wait..that is low!!!
When I went this past Feb/March (had three days in Feb, then the rest in March), when I first got there, I had fri, sat, sun, mon...where the parks were low crowds. Didn't need fast passes for anything. Then by Weds, the more guests started showing up because of some Cheerleading Champions were at WDW for something..not sure what, just know it was invaded by cheerleaders.
So alot depends not only getting there in the value season, but there can still be some kind of events that draw a large crowed, on the weekends especially, then after the weekend the parks get low again.