I thought I'd written about this already when the fansub of episode 1 surfaced in October this year, but apparantly I didn't.
Another landmark series, GeGeGe no Kitaro is based on the manga of the same name by Shigeru Mizuki. There have been 4 anime series in 1968, 1971, 1985, & 1996.
The 1968 series has some early Isao Takahata work, the 1971 has more Takahata work with him contributing the OP and ED. Interestingly, for me, is that the 1996 contained early work from Mamoru Hosoda (Digimon Movies 1 & 2, One Piece Movie 6, The Girl Who Leap Through Time).
GeGeGe no Kitaro concerns the relationships between Yokai and humans. Yokai is a fairly broad Japanese folklore term to describe a number of supernatural creatures, which is reflected by the wide range of creatures depicted in the series. Kitaro is one such of Yokai, but unlike many of creatures appearing in the series, protects humans from the more malicious Yokai. He is a one eyed child, with hair covering his left eyesocket, and possesses a range of supernatural powers. He is invariably accompanied by his father, who following a bout of body eating disease is simply an eye (with tiny arms and legs).
The design of the central character, Kitaro, echoes through manga and anime following GeGeGe no Kitaro, for example, Sanji from One Piece, and more pertinently, Ginko from Mushishi. In many ways Mushishi uses the same raw material as GeGeGe no Kitaro to different ends.