Parasyte
This is the classic Tokyo Ghoul rec because both follow a normal student whose body becomes part-monster, forcing him to question humanity and survival. Parasyte is more philosophical and controlled, but the body-horror identity crisis is almost exactly the same hook.
Attack on Titan
Both shows use man-eating creatures, fear of the other, and a protagonist who becomes connected to the enemy side. Attack on Titan is larger-scale and military-focused, but the horror, transformation, and moral ambiguity overlap strongly.
Ajin: Demi-Human
Ajin shares the hunted-monster identity setup, government experimentation, and a protagonist forced into a hidden conflict after discovering he is not fully human. Its CG look is different, but the paranoia and persecution themes match Tokyo Ghoul well.
Deadman Wonderland
Both have violent secret systems, body-based powers, gore, and protagonists trapped in a brutal world they barely understand. Deadman Wonderland is more prison/death-game focused, but it carries the same edgy survival tone.
Devilman: Crybaby
Devilman: Crybaby shares demonic transformation, violent sexuality, social collapse, and the tragedy of becoming something feared by humans. It is more apocalyptic and experimental, but fans of Tokyo Ghoul's human/monster conflict often see the similarity.