I don't like this manga. I think it's overrated and very poorly written. I've no idea how it receives 10's and 9's from other people, I simply don't get it.

>Story
The story in this manga is actually... decent. It has a cool and relatively unique premise, and it's (sometimes) interesting to see what happens next. However, the author has no idea how to properly move with it. The structure of the story itself isn't dynamic at all, it's too slow for its' own setting and there's a lot, and I mean A LOT, of filler and just stuff that isn't very interesting to look at in a world where Parasites exist. Also, apparently, now that I have finished this manga, the author doesn’t even want to come up with an interesting explanation to Parasites, dismissing their existence to “lol they just came from space”. 5/10.

>Art
It's very bad and disappointing, and the few color pages at the beginning of each volume don't save it. The art is bland, everything feels so empty and soulless most of the time because of the lack of backgrounds. All we get is characters in an actually neat-looking artstyle in front of a white square (https://i.imgur.com/fzG6Lrv.jpeg - perfect example of what I'm talking about, laziness like this is all over the place). Riveting. Is this your award-winning manga?
While I'm on the topic of art, I'd like to touch up on the subject of the designs: they're repetitive as hell. I mean, come on, the mangaka creates a world in which there are intelligent parasites that can shape a human's head in any way, shape, or form they want once they inhabit it, and all he does with that is just draw the samey-looking stripes and blades over and over again. There was a breath of soul in terms of design somewhere near the beginning where the characters meet a Parasite-infested dog that transforms his head into a pair of giant bat wings, how cool is that? I wish this manga had more unique and interesting stuff like that, but, unfortunately, the mangaka doesn't seem to share my wish. 3/10.

>Characters
WHOOOOO BOY, HERE WE GO! Lots of spoilers in this bit, so be sure to skip it if you still want to read this manga.
The characters here are one of the stupidest I've ever seen in a manga. And to explain why, I'll just write about the two examples which frustrated me the most:
1) The case of the sukeban girl (I forgot her name because of how bland of a character she is, more on that later). So, you're trying to tell me that when there are rumors of Parasites going around all of Japan, that when these rumors are being even further explored in national television, that when the MC tries to tell this girl the truth about Parasites and actually explains what they are in great detail, that when said girl can literally SENSE THEM WITHOUT KNOWING WHAT SHE EVEN SENSES OR WHY, SHE DOESN'T BELIEVE THE MC AND SIMPLY DISMISSES HIS WARNINGS!? I'm sorry, but this is atrocious. To top it all off, because she doesn't believe the mc, she proceeds to die right in the same chapter by the hands of a TOTALLY RANDOM parasite-infested human. Absolutely brilliant.
And when she dies, am I supposed to feel sorry for her? Am I supposed to feel sorry for her because she's in love with the MC and is jealous of the girl he's going out with? Am I supposed to feel sorry for her because she got an "embarrassing" dream about the MC once? Those two things are the only things I remember about this filler of a character.
2) The case of the detective (guess why I don't remember this guy's name either). Alright, I can give the girl the benefit of the doubt, maybe there is some human out there stupid enough that wouldn't believe in the existence of Parasites in the sort of sutiation she is, but this guy? This guy? You're telling me this guy only "half believes" in their existence WHEN THERE WERE TWO OF THEM RIGHT BEFORE HIS VERY EYES A DAY AGO THAT ALSO THREATENED TO KILL HIM!? He got told not to meddle in this kind of business by two people: his wife and a woman he fears, and he still goes to investigate the matter of Parasites further with the help of his detective friend. To top it all off, not only have the humans told him to buzz off, one of the Parasites that he saw ALSO told him to mind his own business. And only when his detective friend gets killed by a Parasite, only then he realizes that hey, Parasites are actually dangerous! Who would've thought? God, what a joke.
The main villain of this manga is laughable. He barely gets any development, he barely has his ideologies shown and the final fight with him is just extremely underwhelming. Then again, at that point I was speedreading the manga because I was so bored of it, so maybe I did miss a few crucial points of his character.
But, it's not all that bad, I found the MC and his partner relatively interesting. The MC's development in partucular was interesting to watch, so there's that. But even he isn't safe from mediocrity, because he only gets a clear-cut goal by the 38th chapter, which is more than half of this snoozefest. Unfortunately, even with his flaws, I think that Shinichi is the only decent character in this manga. Every other one is just a stupid device to incite forced drama in the story. 2/10.

>Enjoyment
I didn't enjoy this after the first few chapters in the slightest. This manga is very stupid, and it really boggles my mind how stupid it is. The mangaka expects us to care about characters when he can't properly set them up for us to care about them. The art and the general designs are too boring for the premise the author created, becoming more and more repetitive as the manga goes on. I honestly hated it. The underwhelming villain, the stupid characters, the bad art that gradually got worse and worse (honest to god, defend this https://i.imgur.com/ECj2fQo.jpeg), it's all just terrible. 2/10.

>Overall
The story needs to be more dynamic in order for the story and the world to work and coexist. The art is borderline painful to look at. The characters are stupid. I didn't personally enjoy it, and I think it's highly overrated. What is there to look for in this manga when the only good thing about it is the distinct atmosphere of the 90's it has? I really just don't get it. 3/10.