It seems that the rain has the biggest effect on the parties versus crowds. We went on Friday, 9.16. Crowds were light but we did not have a good experience. In the end, we asked for refunds.
We did some trick or treating after we arrived. Got dinner at Pecos Bill's. The waits were pretty long for that and there was no seating. There was a sign up for mobile order but they weren't using the service.
The lines were short for the rides but we only got to do 2 of them. On Pirates, our boat took on water but never sank completely. Those of us in the back rows had water pouring over the sides drenching our pants. I reported it so they could have the boat checked out or just not put so many people in each boat. It was shoulder to shoulder in every row. The other ride we did was the Peoplemover. It stopped twice while we were on it.
Because of that we were late to the fireworks. Because of the crowds not being to heavy, we were still able to find a spot after the show started where we could see the fireworks blasts but not the castle at all. We waited for the 10:45 Hocus Pocus show which was delayed and then they only did the closing number. We tried to exit into Liberty Square after but they were forcing people into Fantasyland. We circled back to the hub to find a spot for the 2nd parade which was also delayed. I knew I was going to be disappointed when I saw the first group of performers come through. Not only did the Headless Horseman not ride due to the "wet streets" (by this time they were completely dry), but the performers were just walking the route and waving.
By this point, we decided to wait the hour at guest services since we didn't get a chance to do Haunted Mansion, Magic Shots, see any of the entertainment as it was supposed to be, and were still wet from PotC.
It sounds like Sunday night was much better.