Mirai Shonen Conan (Future Boy Conan) (1978)

This is the first TV series that Hayao Miyazaki directed. The show expresses hopes for the purification of people's hearts and the hope for our future without being preachy ever.
Multi-talented Miyazaki Sensei already proved what he could do with this series, doing the character/mecha designs, storyboards, and animation itself.