Final answer:
The Upanishads are the later addition to the Vedas that are more valued in Hinduism, forming the philosophical foundation with deep metaphysical insights.
Step-by-step explanation:
The Upanishads, a later addition to the Vedas, are highly valued in Hinduism. There are 13 principal Upanishads and over 100 minor ones, composed in a period between 800 and 200 BCE. They are composed in a mix of prose and verse and are known to reveal esoteric doctrines about the true nature of reality, which goes beyond the realm of sense perception.
The Upanishads have become the philosophical core of Hinduism, encouraging deep metaphysical thought. The epics such as the Mahabharata (which includes the Bhagavad Gita) and the Ramayana are separate texts that depict important narratives and teachings, but they are not the Upanishads.