This is one of the most important manga in history. I am not saying this lightly. Even if you have only read a select few popular manga chances are most if not all of them are directly influenced by Devilman. And if not than chances are the authors drew inspiration from another work by Go Nagai. I am of personal belief that anyone would benefit from exploring the influences of their favorite works, but many tend to be put off by older media. This raises the question, is Devilman still worth reading 50 years later?
Simply put, yeah. Devilman is as good as it is important. Go Nagai has a running fascination with monstrous heroes and villains who appear noble. He takes inspiration from the Divine Comedy and Paradise Lost, but rather than letting christian dogma shape his world he transforms the iconography fitting to a story about the cyclical nature of war. Demons ruled over earth, the intro tells us, and they appear to be crawling back up from hell. The main character is a fusion between a human and a demon, will he become a solider for either of the sides or try to unite them? Is there any hope in trying to bring resolution to an acient conflict between two sets of people claiming the same land?
This short manga, only totaling to 5 fast paced volumes, manages to discuss a plethora of big issues while also managing to be incredibly entertaining. This isn't a slow philosophical artsy type of comic, guts will be flying while demons beat the shit out of eachother. While probably the least horny Go Nagai manga but it still is packed with goofy jokes, you can see its made by the guy who invented ecchi. The art might at first appear to be a bit dated, once you accept it you'll see that the story is packed full of incredible stylistic flourished for the time, very solid paneling, and imagery so striking it is still being referenced in mainstream anime.
While the ideas and plot encompass a lot, fundamentally it is a story about three characters. Akira, torn between being a human and a demon. Miki, a childhood friend who pushes Akira towards his kind and human half. And Ryu, another childhood friend who pushes Akira towards embracing his demonic side and fighting. This trifecta is so well established in the collective subconscious it has gone on to influence some of the most beloved dynamics in this entire medium. One could say any anime had its Akira and Ryu, Evangelion has Shinji and Kaworu, Berserk has Guts and Griffith, JoJo the Joestars and Brandos. To describe every similarity to Chainsaw Man would take an entire novel. It is worth it to read this manga to experience one of the best paced stories in the medium, one of the most important comics in general, perhaps the best ending to any story every.