NYE is certainly the busiest day of the year at Epcot but it can also be the most fun day if you let it.
The key to enjoying it is not going in with the mindset that if you don't get on a lot of attractions you're day is ruined, because you will not get on a lot of attractions; that's just the way it is. Take a break whenever you can since it will be a long day and just grab a drink and people watch. Pace yourself and enjoy the food of World Showcase. Grab some ADR's for both lunch and dinner because counter service locations will have epic lines all day. After the 6PM IllumiNations the party begins and despite the crowds it can be a whole lot of fun if you let it be. I've gone every year for the last 10+ and not once have I not had an amazing time. And the NYE show is without a doubt the very best fireworks show performed at WDW each and every year. Outside of a bad weather situation (I can't remember the last one) you are in total control of how much you enjoy it. If you are complaining about crowds all day, and complaining about lines all day you'll be miserable. If you accept it for what it is and ride it out throughout, it is one of the most amazing places on the planet to experience NYE.