This is a hard-to-watch show. It's very dense in material and if you don't pay attention closely then it won't make sense. I've seen it three times and each time I've gained a deeper appreciation for certain characters.
This show isn't for everyone, it's hyper-gory, extremely sexual, and aggressively dark. That said, many of the negative reviews aren't given for that reason. Some reviewers have cited a lack of character development, a rushed story, and an excessive focus on female nudity.
For character development, all the characters have dynamic lived lives with varied pasts. We are only given glimpses of these interactions and it's very easy to overlook these tidbits of information. The show has some twists, but all of them are hinted at and are character-based. This seems like textbook good writing to me.
The story is a condensation of what could fairly easily be four times the material. The animators and writers compensated by making scenes convey several character narratives simultaneously. If this was spread out more then it would be more digestible, but the chaotic dense nature of the show lends to the material it's portraying. Characters are given information and sometimes forget to follow up on it, like clearing internet history because they have other more important things happening. It's a chaotic jumble of lives woven together to illustrate a story remarkably efficiently. I honestly think that if you catch most of the material they show then you won't complain about the length of the show. There are plenty of shows where you can skip episodes and turn your brain off to enjoy it. This show requires some active thought to not be a confusing mess.
I'm not a fan of excessive sex/violence. It fits the scene but I think I would have enjoyed it more if they toned it down. There are scenes where men are sexualized, not as many as women, but I think it's unfair to say the show is sexist because there are more scenes of women masturbating than men (but also more scenes of gay male sex). Tonally it makes sense, but I would prefer it being toned down.
The one gripe that I can't argue against is the diehard Devilman fans who don't like this presentation of the story. It's hard to enjoy a retelling of a show/comic you enjoyed a great deal, particularly when it takes such liberties, but these grievances come more from a place of what the show isn't than what it is, which feels unfair. The show does
Other features:
Animation is highly unique. You can tell that the budget was limited for certain scenes and expanded for others, but if you can accept a different art style you should be fine.
The score is very moving and the music helps heighten the emotions wonderfully.
Fight scenes feel very visceral, and enjoyable. I don't love 30-minute slugfests where no one is really hurt, so the quickness to blood and injury helped heighten the stakes.
The symbolism and ending can be interpreted in different ways which I think is good. It allows for a more personalized telling depending on what your preference is. You pick up on the hints that align with the ending you like more and will see that one as canonical, while the ending you would enjoy less is likely the one you won't initially pick up on.
Overall, a 9.5/10.