You took a leap in the right direction. I haven't really tried to build much of a sprite like this, myself. But there are some interesting differences between your sprite and those old FF classics that sort of pop out as large differences.
The largest of which is the size/shape. FF4 sprites seemed to be mostly 16x16 square and FF6 worked off of a taller 16x24 template.
Your sprite is now 14x27. Not a large variance to be sure, but on sprites of this size every pixel can make a huge difference in the overall item.
Your sprite has a very slim and very tall look to it. The waist is as narrow as the neck/chin. The length along the dress is long, flat, and unnecessary. Cutting a couple pixels there or redefining them to give your character more shape would probably help a lot.
You also have large chunks of solid color patches on the clothing, face, and hair. More shading placement will correct that. Look at the way the colors were used in the old sprites to form shape. At this size you really won't see the shadows.
Your shading and solid color is also really pulling forward the mirror-like way you designed the sprite. Split her down the middle and she looks almost identical on both sides. The FF sprites did this too in their standing poses, but they had enough shading/highlighting going on that you had to look closely to notice it. Yours feels statuesque in comparison. The eyes sort of sweep across those solid blocks and immediately pull the shapes out and reveal the mirror pattern.
Another issue that is pulling yours away from the feel of those old sprites is the angle. Your sprite is looking directly at us. FF sprite eyes were placed lower on the face to make the sprite seem like it was looking forward of itself. (Also the eye color does blend with the hair to sort of muddy the face up to the observer.)
Hope these observations help.
