I love her with her hair up. IMO, her face tends to look a bit too broad, or puffy, when she wears her hair down.
She has renewed the whole concept of the chignon. She is very interesting : seems very classic, but always with a bit of fantasy added to it, and that gorgeous, gentle smile of hers.
I wish more princesses found her inspiration in Mathilde; she never disappoints. I like her bold choices, yet always classy and feminine. She is definitely underrated as a fashion icon. Maybe one day, people will study her clothes, hats, hairstyles, etc, and they'll go, Gee, I never knew Princess Mathilde had such an original style.