Essentially the Dessert Party is a paid fireworks viewing accompanied by a dessert buffet, located at Tomorrowland Terrace. We did it on our most recent 2014 trip.
While it was a nice little experience, it's probably something I would do not again. At least, not within the next 15 years. We got in line an hour early (which I highly recommend doing if you book it) so we were one of the first to be seated. We went to the buffet right away to grab our treats, and only just 10 minutes after us a bunch of people arrived and got in line as well. They do run out of desserts and they run out fairly quickly. People did not take things in moderation and I saw some people with two, three plates, and these were not people who were selecting for young children, either.
The view of the castle is okay. You can see all the fireworks just fine, but there's a giant tree in the way and you can't really see the Castle Show. People do go up to the balcony but this was no huge issue, there was plenty of room for everyone to stand up there. Some people did remain at their tables as well.
Overall while it was a fun experience, I didn't find it worth it. It just isn't the same as watching Wishes from Main Street, and yes, waiting forever to get good seats can be a huge hassle, but to me it's all part of the Disney experience and it isn't Disney without Wishes. I kinda felt jipped out of Wishes, actually. It just wasn't the same. The desserts themselves were fine, they had a good selection. But they did run out and while they did refill it, you really only have a good half hour to nosh on your desserts before you have to find a spot at the balcony to watch.