I think for overall this expansion's card arts are really good and fitting in the already existing style. They look colorful, yet they capture the essence of the snowy wastelands.
My favourite card art: Galakrond, the Tempest's final form. The color choices are mindblowing, it looks so action-packed.
The worst card art (in my opinion): Dragonrider Talritha. It looks really messy, it's hard to figure out what is actually on the card. The colors are all over the place.
What are you favourites and least favourites?