We went on Halloween night this year, and it was crowded but not unbearable in any way. We did not ride a single ride (since we were there for 3 days we decided to focus on the special events of the evening instead). We hit every trick or treat spot, including all 3 treat trails and they were no where near running out of candy, even late at night. We also did 3 character greeting spots: Playhouse Disney for Handy Manny, June & Annie (from Little Einsteins), Golden Dreams Theater for Lady Tremaine, Anastasia and Drizella (Wicked Stepmother and Stepsisters from Cinderella) and the Ampitheater for Mickey and Minnie in their Halloween costumes. We waited in line for M&M for well over an hour, and I am not sure I would do that again. We also met the Queen of Hearts, Bowler Hat Guy (Meet the Robinsons) and Cruella DeVille while waiting in line for the mice.
We got there right at opening and the 3 character greetings (we skipped a fourth one that was just over the bridge by Ariel's Grotto that was princesses) plus trick or treating and the character calvalcade mini parade took us from 7:30 until 11:00. We could have stayed 30 minutes longer and ridden a ride or hit some of the treat spots again, but we already had way too much candy and we were tired.
Probably the best parts for us were meeting the Cinderella characters--they were wonderful and perfectly in character, and the mini parade. They did a parade stop right by us and my DS and I got to go out and dance with some of the characters. We finally met Daisy Duck this way and we had a great time!
I think that the party is well worth the money and we will return next year, but we will visit the dance parties instead of hitting every single candy spot. After a week or two of picking at it, I ended up taking the rest of the candy to my office and it filled a huge punch bowl! I liked getting the apple slices and we ate many of them over the rest of our weekend at DL, but we ended up throwing a bunch away too, so it was pretty wasteful in the end.