Well, most romantic stories are made for drama. They focus everything around it, pretty much everything that happens is for the sake of that romance. And that restricts storytelling quite a bit. Even worse with the many manga/anime where it's about 2 people who like each other getting together. After the initial setup, it's all about stalling it until there's no legs anymore, then ending it by having the characters come together.
If romance isn't the main focus of a story, it's a lot easier to make it better. After all, there's more aspects to someone's life than just romance. And you can build up to those moments as well.
Because of this, I think a good romance is found far more often in stories that don't have romance as the main focus in the first place.