What was she other than a whiney White Mage stereotype? That's all she was to me. I don't see the attraction. Millenia was at least a cool idea, an alter-ego that at the end wanted to help out. Even the little robot chick was more interesting -- she developed into something more.
That's one reason that I never got into Aeris. Aeris was the stereotypical "sweet white mage in love with the hero", and never seemed to have a thought contrary to stereotype. I don't want to stab Aeris with a fork, but that's a big turn-off in terms of likeability for any character.