My parents and sisters went in Sept for free dining. Basically their experience was crowded restaurants and value resorts, but very short lines for attractions in the parks.
They stayed at Pop and thought the resort was packed and the busses were always full, but the longest attraction line they saw was 30 mins-- for Soarin. We've stayed at Pop twice around Memorial Day and the busses were not bad, but we saw two hour wait times at many attractions. When we go FP and getting to a park at rope drop is essential-- my parents did not feel that way about late Sept.
They did say they waited quite a while at most of the restaurants. Some meals took 2.5 hours. They had the deluxe dining and did two TS meals per day. The meals took quite a bit of time, but they used them as their breaks to sit down and get out of the heat instead of returning to the resort mid-day.