All I can say is "Wow"
The story revolves around a species of supernatural creatures called "Mushi," that are often the cause of paranormal activity or even prosperity and disease. A varied range of behaviors from a varied range of creatures. Not everyone can see these ghost-like insects, but they effect humanity's way of life in great ways. A Mushishi is a "Mushi Master" who can see Mushi and try to help those affected by them, as well as study them for research purposes. Ginko, a Mushishi who seems to be out of place in time (he wears a white button shirt, loafers, and slacks, while other people wear traditional period clothing), is the main character of the story, visiting different villages and characters in every episode.
The thing that's wonderful about this story is that it's basically a collection of mythology and folklore wrapped up around one character who experiences and studies it all. Every story has a moral or deep theme about humanity involving these strange creatures, and every episode ends with a hauntingly beautiful message or image.
I was introduced to this series about a year ago by a dear friend of mine and have been obsessed with it since. It's funny that only now do I finally finish off the 26 episode run and get around to reviewing it. I guess I just didn't really want it to end. There's really no other series quite like this one. And I have to say that I'm probably going to go out and get the manga that this series was based on as soon as humanly possible.
For those that are fans of Hayao Miyazaki films like "Spirited Away," "Ponyo," or "Howl's Moving Castle," this is the same vein of animated fantasy, but with a more mature touch.
Not to mention the opening credits and theme song are gorgeous.