Mickey's Not So Scary Halloween Party takes place all over the Magic Kingdom. The vast majority of the rides will be open, and since a limited number of tickets are sold for the party, the lines for the rides are usually quite manageable. But that's not the half of it.
There will also be trick-or-treating stations all over the park, dance party areas, a special parade, special fireworks, and lots and lots of characters. Some of the characters are ones that don't appear in the parks during regular hours. And almost all the characters will be in costume!
If you'd like to find out more detailed information and trip reports from other guests, go to the website allearsnet.com and click the search button (in purple, near the top right), and search on the word "halloween." You'll find many halloween party articles there.
Hope you have a great trip!