I really like the fact that Go Nagai stopped abusing screentones for the later half of Devilman and stopped leaving around random, minor anatomy errors. Shit was ugly as hell even though the last few chapters are impressive by 70s weekly manga standards.
Oh well, he had to churn out five different fairly long chapters for different series a week back then, so I guess I'll look past a badly drawn hand if the writing is awesome. You can really tell he stopped rushing things at around volume 3.
Plus his work for Violence Jack was on par with Fist of the North Star so the fucker definitely improved really damn fast