I saw it more as adding depth to a story that needed it to become a full-length film more than taking extreme liberties with it. All the core elements of the story are totally unchanged. Plus, the story is completely vague in lots of ways. It basically says the people of the Earth had "corrupted" it, that they were "wicked," turned to "violence," etc. Aronofsky's interpretation of what that might mean seems totally reasonable to me. Furthermore, fallen angels are in the bible. Aronofsky just decided to interpret "chains of darkness" (or whatever the verse said) as encased in stone. And lastly, as khorum said, pretty much all of the patriarchs in the bible are assholes.