I like this work at several different levels. First the composition. There is a strong diagonal in the background running from bottom right to top left and this draws the eye in that direction. As it does, you scan the head and hair of the subject and this seems to emphasis the movement of the head. The head itself lines up with this diagonal and the eye is drawn to the movement of the hair.
The colour is subtle and muted with just enough saturation to appreciate the colour balance between the blue dress and red hair. The saturation in the background is enough to convey a feeling of forest without taking away from the main subject. The overall effect is of an oil painting from the romantic period at the end of the 1800's.
Finally the pose of the model expresses a refined elegance and dynamic emotion.
This is a really striking image, wonderful.