I did the party Saturday night. In summary, it was okay but I wouldn't do it again at the current price and setup.
You check in as early as 7:30 on the left side of the Worldshowcase mechandise building nearest Mexico. They give you a writsband. You then wait in a holding area behind that building until 7:45. The event then is on the right side of that building in front of the lagoon.
Once open you are free to help yourself to the drinks and desserts. The "sparkling wine" seemed to be champagne type items (I did not partake in those) which they pour for you.
There is a table with coffee, tea, lemonade and ice tea as self serve. Then there is a large table with the desserts.
The desserts are themed to some of the countries; baklava, French pudding, tiramisu, donught (not called that) and a spread of fruits such as pineapple, strawberries and melon. These are all served all night.
My complaint: no seating. They only had high top cocktail tables and not enough for everyone that was there. It was an hour and a half of standing. Not a big fan of that as there was LOTS of extra space to have had sit down tables.
So, glad I was able to try it and the view of Illuminations was excellent. However, the Magic Kingdom's dessert party is superior. The Epcot one would have been more better priced at around $25-$30 for what it was IMHO.