Its Go Nagai so no one should be surprised if one of his works is ecchi or in this case ends up containing nudity, violence, rape, more rape, gang rape etc. The whole thing is a schizo mess. The art sometimes has some good panels and other times not so good. There's also a shift in art style from the first 3-4 volumes to the later ones that look closer to Go Nagai's style, which makes me think that the early volumes had a lot of work done by his assistants (I think he at one point had a large stable of them).
The story is an even bigger mess. In the first 3-4 volumes Jun our lead character becomes Devilman Lady. She's a former Olympic athlete and a teacher (in the anime that I saw like 15yrs ago she was a model). She's becoming increasingly violent and ruled by her baser emotions, she's worried about losing control and wants to fight devilbeasts as a channel for her aggression. This would be ok-ish except for the monster raping stuff done for titillation and drama.
Then someone must have gone up to Go Nagai and told him "hey this is too grim it needs some humor". At which point it turns into a slapstick buddy cop pseudo comedy (ouch my neck just got whiplash). Yes Jun joins the police force, while working at school, then is working at an embassy but still working at the school? Who cares if it makes sense right? Jun also gets a personality change, before she was mentally tough (she sure told off those Karate punks before becoming a devilman) and physically powerful but then she turns into a scared wallflower that needs rescuing and constant reassurance. Around this point someone goes up to Go Nagai and says "you know what this manga needs to boost sales? It needs the original Devilman!" And we return to grimness and let's throw in some wacky Christian stuff. Wait what happened to the pseudo-science explanation for Devilmen and Devilbeasts? Now we are doing pseudo-religious crap? Ugh, and who's story was this about anyways? I thought it was Devilman Lady. Oh, and nothing makes a woman feel better after being gang raped than having sex with some hot guy (WTF??), at least according to Go Nagai.
This is the easy stuff to criticize, the story has so many problems that its not worth going on about. That's not to say there wasn't some potential early on with the monster of the week early volumes. The story about her rival in swimming had some compelling moments and the story with the bullied boy was adding a little bit of nuance about who the real monsters are (hint: its the humans duh!). Unfortunately, a few small moments of possibility get crushed under a ton of garbage. I have no problem with violence, nudity or gore, but if its stupid aaand boring on top of that then its a problem. I made it thru about 11vol. of this trash before finally giving up. Devilman Crybaby it ain't.