We went to the party on Halloween night. We knew it would be a zoo, and so had no objectives to be met, such as having to go on a certain ride, or have our picture with a certain character, etc. That made it less likely we'd be disappointed, and we did have fun, and enjoyed short wait times on regular rides, and an eventual 7 Dwarfs photo after three visits to the line.
In my opinion, there's not enough "special" to be worth the high cost of the "special event" ticket. Although the Hallowishes fireworks were spectacular, I thought the parade was kind of short, and only a couple floats were Halloween-specific (I don't count a Halloween banner hung on Peter Pan's pirate ship as a specialty Halloween float parade entry). The headless horseman at the start of the parade was actually the best part for me. Most special experiences like photo ops and character meet and greets had ridiculously long lines. You wouldn't have to struggle to have spent the bulk of your Halloween Party time on the line for a photo with the Dwarfs and queuing up in advance so you had a chance of seeing the parade not six people deep. For the first hour or so of the party, the lines for a handful of sponsor-provided everyday candy stretched a long ways. They did move quickly, but we weren't tempted to wait in any of them for a Snickers bar.
During the transition to the party (between 5-7pm) there was a brief taste of the "old days" when there used to be genuine slow times at Disney parks when you could happily scamper from ride to ride getting on nearly everything with little to no waits. We were relieved at least there was no line at the Peoplemover. On our last few visits, not during prime time, there were still lines at Peoplemover midday. You KNOW it's a bad day when there's a line to get on the Peoplemover!
We thought it would be fun to have our picture taken with the 7 Dwarfs and their buckets of jewels once we saw them set up for photos. The first time we checked the line the estimated wait was two hours. What? That's an awfully big chunk of our paid "party time" standing on one line. We left and came back after the first parade. Because we didn't get in line early for the parade, we got what we expected with a swarm of people to have to see over, who all started standing on benches and planters and putting their kids on their shoulders as soon as it began and that was ok, because we'd already decided to watch the later parade instead. So we saw the tops of the taller floats go by. Back to the line for the 7 Dwarfs picture. It's now "only" an hour, but we didn't want to risk being in line when the fireworks went off. After the fireworks, we went back once more, and this time the wait was a half hour, which by then we were ok to spend because we'd seen and done most everything we could do. If you were able to stay awake for the last parade, you could get a decent spot to watch even minutes before it began, which we did.
This was a Disney bucket list item for us, but I wouldn't spend the money again because I think there are just too many tickets sold to allow you to really feel like you are in a special event. Mickey's Very Merry Christmas Party used to be truly special as in addition to a lot of party exclusives that you couldn't do or see during regular park hours, there was space to breathe between people and little or no lines for anything, and no six-deeps at the parade even last minute. I doubt it is like that anymore because somewhere along the way, Disney discovered people would keep buying higher and higher priced tickets to special events anyway, even if they were packed to the gills. And then pay for "special experiences" like dessert parties at their special event.
I've read other people's reviews who didn't think the lines for the special Halloween stuff was bad, and I wish I'd known who they were, because I would have followed them around! All in all, we did enjoy the party, but could not make a case for it being worth the premium. We visited without our kids, though, so we're not factoring in the pleasure kids may have despite the crowds that parents would determine legitimized the cost.