We can learn much about Mesopotamian culture from this epic. First, we see that one strong male leader, assisted by a counsel of city elders, was the traditional form of government. However, there seems to be a real concern with the rights of the citizens, as Gilgamesh is expected to be a just ruler. The outrage over his abuses actually leads to the creation of Enkidu in the story.
In The Epic of Gilgamesh, the presentation of religion is similar to what Greek and Roman authors would depict a thousand years later. First, the Mesopotamians were a polytheistic society. Many gods are attached to natural phenomena or occurrences: Shamash is the god of the sun (and his wife the goddess of the moon), Ishtar the goddess of both love and war, Ea the god of water and the arts, and so on. This is common in polytheistic religions.
Second, the gods are heavily anthropomorphized. They have relationships, they pick favorite mortals to guide (or choose their least favorite to destroy), and they fight among themselves. When Enlil chooses to destroy mankind in the Flood, Ea saves Utnapishtim by telling him to build the boat. When the Flood is at its fiercest, Enlil is safe within his palace, while the other gods are cowering around the gates, soaking and miserable.
There is gender division suggested in the culture/religion as well. The king of gods is male, which suggests a patriarchal society. Yet Ishtar is a major goddess, controlling both love and war, and the city of Uruk is dedicated to her. Because she controls two aspects of human nature ruled by emotion, we might infer that Mesopotamians associated women more strongly with instinct or emotion than reason.
The images of the afterlife are strange. The underworld is certainly dark, and it appears that all souls alike are trapped underground to shuffle about like birds. Because this is such a fragmentary look at Mesopotamian beliefs, it is difficult to form an accurate picture of their vision of the underworld.