Above all, this is considered a merchandise event. There have been previous posts where people said they went last year and wouldn't go again. A group of friends and I went last year and are doing the middle package this year. We love Haunted Mansion, we love the merchandise and can't wait until October.
There are only three rides open during the party - Splash Mountain, Big Thunder and, of course, HM. The buffet was very good and there were a lot of selections. The highlight of the evening for many of us was the appearance of the headless horseman (2 or 3 times). He starts MNSSHP but he just rides through non stop. Here he actually stopped. He had the horse rear up and when he wheeled his mount around you could see sparks fly. Very cool! They also had some picture opportunities (in a doombuggy - cost extra) and fortune tellers.
As I said, we enjoyed it and are looking forward to this year!
I went last year & had a blast! The best part was meeting some DISers and friends from a HM board I visit. They have expanded it to a three day event like the HMH at DL this year,and the most expensive package has sold out. Check out Disney's official site for more details: http://psc.disney.go.com/eventservices/disneygallery/calendar.html