I don't LOVE the rug. but I think the green curtain, built-in shelves filled with books and the (presumably) sliding ladder are wonderful. Its missing a fire place, lots of cozy blankets and an oriental rug!
Book Nook in a fireplace that is no longer usable. Very creative use of space. Just make sure to clean that fireplace well before putting any books in there and to seal things to prevent water damage or pests from coming down the chimney.