“Noah” is best interpreted, I think, as a modern cinematic midrash on the Biblical tale. The midrashim—extremely popular in ancient Israel—were imaginative elaborations of the often spare Scriptural narratives. They typically explored the psychological motivations of the major players in the stories and added creative plot lines, new characters, etc. In the midrashic manner, Aronofsky’s film presents any number of extra-Biblical elements, including a conversation between Noah and his grandfather Methuselah, an army of angry men eager to force their way onto the ark, a kind of incense that lulls the animals to sleep on the ship, and most famously (or infamously), a race of fallen angels who have become incarnate as stone monsters. These latter characters are not really as fantastic or arbitrary as they might seem at first blush. Genesis tells us that the Noah story unfolds during the time of the Nephilim, a term that literally means “the fallen” and that is usually rendered as “giants.” Moreover, in the extra-Biblical book of Enoch, the Nephilim are called “the watchers,” a usage reflected in the great hymn “Ye Watchers and Ye Holy Ones.” In Aronofsky’s “Noah,” the stone giants are referred to by the same name.The film certainly is an imaginative retelling, but I haven't heard much evidence that the elaborations are based on hints elsewhere in scripture, as with ancient Jewish midrash.
Once again, someone who should know better garbles the Watchers myth. In the Book of 1 Enoch the Watchers are angels who fathered the giants on mortal women. The Nephilim are the giants, not the Watchers. And the hymn is based on the "the Watchers and "the holy ones" mentioned in Daniel 4:14 (cf vv. 10, 20; English vv. 17, 13, 23). According to the Enochic mythology (1 Enoch 14:23, 39:12-13), some of the Watchers remained in heaven unsleepingly guarding the throne of God, and this is likely assumed in Daniel, but the reference is to the passage in Daniel, not 1 Enoch.
Earlier posts on the Noah film are here and links.