You can't get into the Sumerian Religion without telling a little of the Anunnaki history.
Throughout historical accounts there are stories that reappear over many ancient texts and throughout many religions. From the Bible, to Indian writings, to Greek Mythology. These accounts seem to borrow from one to the next to give their own spin on how history occurred. Like the tree of Life, to even the Great Flood.
The best way to determine the accuracy of these stories is to find the earliest writings. Which isn’t the Bible, or even Egypt, but Sumer.
I am not an expert on the Sumerians but I have an avid interest and read quite a bit on the subject. I find them to be extraordinary. To imagine that before this society, chronologically we were Neanderthals, is amazing. Almost unbelievable. To go from “Uhg, me want food” to arithmetic and mapping the stars, is unbelievable. Sumer is the first recorded society to date, with recorded accounts from that civilization with knowledge you would think would be beyond their grasp. If you looked at today’s society several thousand years from the future, would the future beings viewing our records think that we considered movie stars and rock stars as Gods because of how we idolize some of them? Granted the Sumerians believed their Gods, the Anunnaki, were consciously in control of the elements and nature. They also believed that the Anunnaki actually scientifically created us into the current Homo sapiens.
According to Ancient Alien Theory, the Anunnaki, and other alien groups, came to Earth and seeded the human race in many variations. This research was lead by Zecharai Sitchin and Erich on Daniken. Physical evidence of ancient astronauts is found throughout the planet, leading one to conclude that different races visited here at different periods in Earth's history, or the same aliens return and set up various programs (civilizations) in which they could remain and experience. These would include: the Middle East, Egypt, India, China, Greece, Mesoamerica, and other Ancient Civilizations.
The Sumerian texts are full of interesting tales that I am not sure if they are accurate history or fiction. Yet, from all fiction there is always a grain of truth, and even a small portion of this being true would be astounding. Plus, why would an entire society have the same point of view concerning their Gods, when by all accounts the Sumerians appeared to be a rebellious lot.
Sticking with the great flood, an interesting tidbit: If Noah was an actual person and not a generalization, he would have been living for a long time before historical records, being 600 years old at the time of the great deluge detailed in the Holy Bible. Noah is sometimes considered to be the Father of wine, and archaeological evidence suggests wine production started as long as 8,000 years ago. This could be an indication of the time in which he would have lived. Following the genealogy from Adam to Jesus, most theologians place the Flood at around 5,000 years ago (3,000 BC), approximately.
The Anunnaki as a species were very human like with families, in-fighting, child births, they could be killed, and with personality traits of good and bad Gods. It is even recorded of a few of them getting drunk.
The bible which itself states that demonic beings who were banished from heaven for failing to bow before God's greatest creation, man; and who were giants in comparison to us ascended from the sky. It then says they interbred with females to create a hybrid bloodline. God eventually destroyed all these ungodly beings although this lays the case that these beings have around since the beginning of time and are not some mysterious race from another planet. Some believe these demonic beings are working in opposition to God and are in fact Demons in today's world. In almost all the exorcism cases there is a little known fact that the victim of demonic possession speaks typically in ancient Sumerian, unlike many Hollywood movies would make you believe they speak Latin even though the language did not exist before Christianity.
Good detailed site about Sumerians and their Gods
More info on the Sumerians
Zecharia Sitchin, Twelfth Planet
Erich Von Däniken, Chariots of the Gods
Dr. J. Allen Hynek