Mushishi... By far the best thing I've ever seen. It has such a beautiful music combined with great art style and a story deserving to be a masterpiece on its own.
Nothing I say will ever show how much I love Mushishi as it takes me to a different world everytime I watch it.
Great if it follows the manga but there's way too many filler episodes especially as the manga had ended over a year ago. Used to be my No.1 anime and now it's in a fragile 10th position.