Genesis 6:1-4 - "Sons of God Took As Wives the Daughters of Men"

Genesis 6:1-4 The consensus among Bible commentators is that this passage is the most difficult to interpret (with certainty) in all of Genesis. There are three main viewpoints (with some variations within each viewpoint). We begin by looking at the advancing context in Genesis, we briefly identify the three views, and I advance the particular understanding that the "sons of God" are (types of?) fallen angels.