Panorama of Hell, Kami no Kodomo Recommendations
Both are first person "confessions" of sociopathic individuals which draw you into their madness. Both have unusual art style in comparison with mainstream manga art style, so if you liked one of them you certainly might like the other. While Kami no kodomo is more drama like and generally drawn in light colors, Panorama of hell is visually very dark and ink strokes are heavy do depict more grotesque setting.
Both manga have psychopathic main characters and first-person narratives, which invite the reader into the characters' madness. Both have unique and bizarre art styles, combined with grotesque imagery and stylized gore, which makes the manga quite similar in plot, style and vibe.