This hat is wonderful! I'm usually an Large/Extra-Large hat, and ordered XL in this case. I was happy I did - it barely fit. The fur is incredibly soft and warm, and the way it wraps all the way under the brim is insanely comfortable. I've worn it in quite a bit of weather well under freezing, including moderate amounts of falling snow, and it has held up admirably! I certainly own nothing warmer or softer. That said, you will definitely want to tie the flaps under your chin in high wind.
As another review noted, these definitely run small! My wife loved stealing mine so much that she ordered a medium for herself (nothing else was left in stock), and it may actually be too small for her to wear without getting a headache.