Final answer:
The Sumerian belief system describes the afterlife as gloomy.
Step-by-step explanation:
The adjective that best describes the afterlife according to the Sumerian belief system is gloomy. In Sumerian mythology, the afterlife was seen as a dark and dismal place where the souls of the dead would reside. This belief is reflected in their literature and religious texts.
One example is the Sumerian poem called "The Descent of Inanna" which describes Inanna's journey to the underworld. In this poem, the afterlife is depicted as a gloomy and terrifying place.
Overall, the Sumerian belief system portrayed the afterlife as a gloomy and undesirable realm.