Final answer:
Neo-Platonism is more a philosophy than a religion, emphasizing metaphysical concepts rather than the personal worship of deities, which characterizes the other options as mystery cults or religions. The correct answer is d).
Step-by-step explanation:
Among the options listed, D) Neo-Platonism is more of a philosophy than a religion. Neo-Platonism was a philosophical system developed as a form of Platonism that later had some religious and mystical influences. It focused on the metaphysical concept of the One, the overarching unity from which all existence derives. Contrarily, the other options like the cult of Isis, cult of Mithras, Manichaeism, and cult of Demeter were all mystery cults or religions with specific rituals, deities, and spiritual practices that offered personal religious experiences through initiation.