We went to
MNSSHP when it 1st started a few years ago (2000 ??) and wow, what a blast! Lots of candy, great sound and decorations and nobody had discovered yet. In fact we didn't even know about it beforehand. It was so much fun we immediately got tickets for another party 4 nights later that week!
Well....fast forward 5 years and plug in the Disney marketing machine and you have still a wonderful setting....but lots and lots of people.
We have been down 4 times for the party since our first trip and have still enjoyed it but, that 1st trip was awesome.
With the bigger crowds each year it is no longer a "private party". I would certainly not do (2) nights each trip as we had done before.
I would recommend not doing a Friday night (as they seem to be busiest) and trying for a weekday.
The cast members have been much stingier with candy and the candy lines were so long last time that we pretty much skipped trick or treating altogether.
We invested our time in rides & attractions as opposed to gathering candy we would have loads of after Halloween anyway.
The tips from previous posters are correct, Don't miss the parade (especially the start), the decorations are great fun, make sure you "experience" Haunted Mansion.
Be sure to arrive when the party 1st starts to avoid using a park day on your regular tickets if that is an issue for you.
They also offer a free (ooops included

) family portrait that you should take advantage of. We've found that waiting till later in the night is best to avoid the long lines for these pictures.
Anyway, hope some of this helps!
