DH and I used to go to WDW in January (not yearly, but several times) and absolutely loved it. Low to non-existant crowds, very little wait time for rides - usually 5-10 minutes, maybe 30 for the really popular major rides and rarely ever needed a fastpass.
Then DD went with me (her first trip, she was 34) in September 2013 and it was extremely busy and HOT and HUMID. Loved being with her for a week, but wouldn't do September again.
Then last January we were invited to go with her and her DH and their two kids plus the other set of grandparents for 8 nights. Loved being there as a family and would go again in a heartbeat if asked, but DH and I have no plans to go back anytime soon. The crowds were bad, and thankfully we did have faspasses every day for the major rides, but wait times for other rides were sometimes 30-45 minutes, and for the major rides like Soarin' it was quite common to see a 120-minute wait. Wow. Things sure have changed. I'm not sure there's any "slow" time at Disney anymore. For us as a couple it's just not as fun as it used to be and there are too many other places we want to go. I'm not saying we'll never go back, but it'll probably be a l-o-n-g time.