Hi!
It's all about the combination of fine dining and romantic atmosphere, but everyone has a different idea of what constitutes romance. We like places where it's quiet enough to talk, they don't rush you through your meal, and the theming is distinctive. So for us, Artist Point at Wilderness Lodge, bluezoo at the Dolphin, Yachtsman Steakhouse at the Yacht Club and Jiko at Animal Kingdom Lodge are good bets.
If you can add in a view of the fireworks, even better! We got a window seat upstairs at Bistro de Paris in Epcot and enjoyed a nice view of the fireworks and a leisurely meal.
If you're OK with the food not being that great, a table at the window overlooking Fantasyland from Cinderella's Royal Table is perfect when you can time it to be there during the fireworks. We've also had a very romantic meal at Narcoossee's even though the food wasn't that fresh or interesting - sometimes, it's just about the mood you're in, I think!
Lots of people think Victoria & Albert's is romantic, but some find it stuffy.... And San Angel Inn in the Mexico Pavilion gets a bad rap, but you gotta admit the faux nighttime-outdoors atmosphere is romantic!
Hope this helps!