Junji Ito isn't a great writer. He's excellent at monster design, drawing strange, gross creatures and gore, but his characters are often flat, boring, and interchangeable. They're just a means to an end, a literary device, a blank slate for the reader to relate to. Their only purpose is to get spooked by the strange, gross creatures Ito is obviously far more interested in.
No Longer Human is an excellent, character driven novel about one man's decent into decadence. Its horror (if you can even call it that) is internalized. A man slowly self-destructs due to addiction, mental illness, and his own nihilism. It's a work of great subtlety and beauty.
Junji Ito's No Longer Human tells a very similar tale, but with many changes that drain the story of both its meaning and nuance. It is externalized horror, because that is all Junji Ito can do. The chapters are episodic, and usually end in a blood bath. I'd estimate that 9 out of 10 indistinct, interchangeable women we meet in this book die horribly within 2 chapters of their introduction. Our drug addled, alcoholic, socially awkward main character is so handsome that he drives every woman (and even some men) he meets to suicide. Yup, it's Tomie all over again.
Why? Why is Ito jumping on the Pride and Prejudice and Zombies band wagon years after that was a thing? Why take a novel about a very personal breakdown and turn it into a manga about...I don't even know. Scary suicide corpses?
In short, Ito sucks at character work, and No Longer Human is a character study. He tries his damnedest to mold it into something scary, but instead we're left with Ito's least imaginative art, and a shallow husk of a story. It's like those old, "spooky" covers Marilyn Manson used to do, classic songs turned into something you might listen to on Halloween for a laugh.