We were in the MK on Memorial Day Weekend three years ago and it was very crowded, hot, and humid. Lines were long and the kids (and adults come to think of it) got cranky. I remember standing at the castle and looking back down main street which was a wall to wall sea of people. If this had been my only experience at the MK I probably would never have gone back. We didn't go to any other parks that day. We now try to avoid high capacity days if we can help it.
However, if schedules forced me to go at a peak time I would still go but just try to time park visits to avoid the worst of the crowds.