This is an often overlooked work of Rintaro and Katsuhiro Otomo. Otomo was the director of Akira, and many of the concepts and visual styles of Harmageon show up in Otomo's later works (including Akira). Harmagedon is considerd by many to be the building block of Otomo's later accomplishments. If you want to see where it all started with Otomo or with his style, Harmagedon and Akira are worth doing a comparison viewing.
Both series have a group of people with superpowers who fight on two opposite sides with obvious purpose, one cause a catastrophe and the another group save the world from that plan. However, the common people does not interfere much in the story.
Genma Taisen is more apocalyptic while Ai City is more biological and cyber.