Day 3 of my 5 favorite things at Disney is all about one of my favorite holidays, Halloween! I can often be a big critic of the costs of Disney's "extras," but I still love Mickey's Not So Scary Halloween Party. When you consider that you can get into the park 3 hours prior to closing in addition to your 5 hour party, all for the around the same price as a single day ticket, that's not completely outrageous. Remember that this is a hard ticketed event which means you do not have to use one of your theme park tickets.
If I had to narrow it down to my favorite thing about the Halloween party, I'd say it's the Boo To You Parade. It truly is the best parade of the year in terms of how elaborate the floats are, the variety of characters on them, the music, and the overall vibe/tempo of the parade. The current show in front of the castle, Hocus Pocus Villain Spelltacular isn't far behind in my favorites. For fans of the movie 🙋♀️, this show is great! The vocal performances, the costumes - just super well done. And oh the fireworks! Hallowishes is a completely different fireworks show from Wishes or Happily Ever After - definitely worth seeing especially if you've been there done that for the other end of night shows.
For character lovers, you have the opportunity to meet rarely (or never) seen characters during the party such as the 7 dwarves, Jack Skellington, and Lotso. You'll usually find them not too far from trick or treat spots too. Oh and then there's the candy ... who doesn't love that and the fact that even adults get to do it! Even better than the candy though are the exclusive treats they release each year, some just for the Halloween season and some just for the parties. Particularly for guests who have visited Disney multiple times, it's always a big plus to get to see, do, or try something new. Oh and there's all the cool magic shots and photo ops that are exclusive to the party (like the ghostly one near Haunted Mansion that's always super popular).
Ride access is of course better during the party because of the intentionally reduced attendance; however, I never advise spending a big chunk of time on rides during party hours (do it the 3 hours prior) because if you do, you'll likely miss out on the things exclusive to the party. If you're all about low ride lines, do After Hours or Early Morning Magic instead.
I would always choose to do the party in true fall (not August). Sweating through the park, trick or treating in broad daylight ... it's just not the same. Arriving to the park in the dark with the smoke machines going out front and the spooky fun vibe and music just really sets the tone. Even without the party itself, the decorations in the park during that season are my favorite of the year. Main Street is absolutely gorgeous decked out for this holiday!