Genesis shows how families grew into nations. It is interesting to see the connections between individuals mentioned in Genesis who became nations of peoples mentioned later in the Old Testament. You can also trace how one person's disobedience to God, such as Cain or Noah's son Ham for instance apparently had far reaching effects that led to wicked nations of peoples God would later judge severely. In Genesis you can also see how certain individuals among the descendants of Abraham had very important influence on a multi-national scale, such as Joseph. Genesis gives a unique perspective on how God sovereignly uses individuals to affect history.
Genesis covers thousands of years of Earth's early history.
We must remember that the writer, Moses, was educated as an Egyptian and this would have included their polytheistic animistic religious concepts. Also, the various other peoples of the time encountered by the Israelites were steeped in idolatry. Genesis and Exodus are very complementary to each other as Bible books. Exodus begins the story of the Hebrew people essentially where Genesis leaves off. Genesis and Exodus possess certain similarities and may be written with a similar purpose in mind.