We were there for New Year's Eve 2004. And 2001 but didn't venture near a park for that one. Too much family. For 2004, we went to Animal Kingdom and had a great time. Not very crowded at all. A bit more people but manageable. After a while, some of our party went over to MGM to finish that up and ended up having a great time and wanting to stay quite a bit longer. My son (22 years old at the time) said that if it wasn't for us and his grandparents waiting, he and his family would have stayed for the festivities. They got top hats and noise makers for the evening. Son said it was very nicely done. He thought that maybe with the ABC TV coverage focusing on Magic Kingdom and Epcot, that MGM was "neglected".
As far as Epcot is concerned, we saw their fireworks from outside our room at All Star. Yes, they do something extra. It's a WOW moment.