I was there twice during that week in 07 and 05 and had two different experiences. Both times were great and we had a lot of fun, pretty much a 0 wait time for the rides that were open but there were a few changes on our second visit that were disappointing to me.
On our first trip, the MK wasn't all that decked out for halloween during the day. The park closed at 6 and then you could not reenter until 7. When we walked in, our jaws dropped. The transformation was unbelievable....in an hour!!! There were also lots of character meeting spots throughout the park including characters you don't normally see, alot of the villans. It was really neat to get pictures with the queen from snow white (her name escapes me at the moment), etc.
On our second trip, the park was decorated all day so there wasn't much, if any difference in the appearance of the park. Sure, the eerie music was there and lights on the castle but otherwise, no changes from what you saw during the day. There was no downtime between the park closing and the party starting do the crowds were much heavier as people were leaving and entering at the same time. Still not a bad wait time after you got off of mainstreet after the parade. And I didn't see nearly as many characters around and none of the villans on the night we attended, just the usuals.
My DDs still had alot of fun and I"d do it again but disney really needs to come up with something a little more....awesome, as you would expect from disney!!
This year we are trying
MVMCP instead....we'll see!