Critique-wise, I can't think of much to say but the bottom half of her hair does look rather stiff when compared to the more fluid lines of the rest of the drawing. Since your style is more realistic than the FMA animators's/Arakawa's, I think a more "natural" looking hairstyle would work better for this piece.
I usually try to keep the hairstyles as close to original as possible with a touch of realism because I've always thought that hair styles were one of the main identifying features of a lot of anime characters since facial structures are always so similar. Hair and clothing seem to be key.
As for the dress... I did this a couple years ago so I can't remember exactly why I did it the way I did... I think it was to show some body structure underneath the dress since the whole piece is so dark, and that's the only way I could think to show some definition to the body without putting in a fill light, which I actually didn't know how to use very well at the time that I rendered this.