Sorry that people were disappointed. I enjoyed it, although it's not my favorite Aranofsky movie. I also could see why he made particular changes to the story, in order to bring out certain parts of Noah's character and personality.
Prophets are always severe, usually in personality and in their perceptions, and for a man to persevere in such a large undertaking while watching humanity die also would suggest he was persistent and unyielding; he had to be. Aranofsky tried to take that to its logical conclusion, resulting in a potentially horrific resolution; it made sense to me and treated the character realistically.
But the nephilim story was changed to suggest a God of judgment and one of mercy as well -- these rebellious angels were damned for coming to earth, but they also were finally released from that captivity. Their plight reflected an aspect of God that Noah in term had to emulate (though he didn't realize it), and so he struggled with the mercy aspect.
Yeah, I almost started to laugh when Crowe began singing ("NO, please, just... NO!") but at least it was an appropriate venue for him... he wasn't supposed to be able to actually sing, and all of humanity was about to die soon anyway, so...

And the song tied in later, it was important to the plot. I gotta say, he brought a lot of weight to the role; he grounded Noah, ironically enough, and provided him substance equal to any stone giant.
Some in the religious community take this movie as a declaration from Satan that he's coming to f-up Christians the way God did to the Nephilim during that the days of Noah. At the bottom of the movie poster, it says something like "the end is near." And, they were filming in the New York area, and filming had to be delayed because of Hurricane Sandy. Get it? The making of the movie Noah was delayed because of a flood. The third thign was that at some point in time during filming Russell Crowe either fell out of a raft and nearly drowned or he got lost at sea or soemthing. I'm fuzzy on the details about that. But it's interesting (at least I thought so).
It started raining when I walked into the movie theater, but hey, I'm still alive.
Jason Statham almost drowned filming Expendables 3, but that don't make him a prophet.