LM, We went last year and are planning on going back this year. You and your family will have a great time. The party begins after the park closes, so its open only to those who have tickets specifically for the event.
Last year I heard that they only open the event to 40,000 folks per night, so you are not faced with especially long waits for any of the rides or events.
There are several locations set up throughout the park where the CM's hand out candy for everyone. And as far as I know, all of the rides are open, but not sure about all of the shows.
Somewhere around 9:00 (if I remember correctly) they have a parade similar to the one they have during the day with the exception of all of the characters being dressed up in costumes, and a ride of the Headless Horseman.
All in all, I would say that this is a great deal. When else can you visit the MK for 4~5 hours with a limited amount of folks, all rides open, decorated for Halloween, and get enough free candy to send the kids into orbit for that price.
I'm sure other folks will have additional input as well.
Oh by the way, when are you going? We will be there for the Oct. 19th party.
Have Fun!
Duane