I watched Noah after both reading the graphic novel (by the same writers/directors of the movie) and reading a number of reviews - mostly negative, and one positive (Christianity Today) - all written by Christians. The graphic novel, admittedly, is better than the movie. It deals better with the themes and characters and I thought it portrayed the Watchers better. I wish the movie tried to do a 300 and be as faithful to it as possible. But they made several - biggish - changes
But no one cares if Noah was faithful to the graphic novel on which it was based. Christians want to know if it's faithful to the Biblical text. Well, yes it is and no it is not.
If you're expecting a straight telling of Noah, it's not going to happen, not in this movie, and likely not ever. There is a reason why every movie about Noah has huge amounts of artistic licence: there's not enough source material. For example, in a TV movie made years ago, Noah saw the destruction of Sodom. If movie makers made a movie "faithful" to the Biblical story it would be a bad movie. And Noah is not a bad movie.
Most surprising to me is how the negative reviewers interpret the movie. For instance, they love to mention that Noah goes "crazy" and wants everyone dead. That interpretation is simplistic - almost idiotic. What clearly happens is that Noah realizes that he and his family are no less corrupted by sin than any other person/family, so why should they repopulate the earth? Sin will only live on! (Noah, being righteous, doesn't want sin around!) At the end he realizes that he can love and have mercy, just as God loved and had mercy on them. One scene near the end reminded me of a type of proto-Akedah. This reversal in Noah's thinking is most evident at the very end where Noah tells is family to "be fruitful and multiply".
The other aspect that seemed to upset people (and I initially dismissed it as well, early into the graphic novel) was the environmental agenda the movie has - and, yes it has one. But unlike other movies, this one serves a clever purpose. The way people treat their surroundings is clearly the way that they also treat their fellow man. The destruction of creation (clearly evident throughout the film) is a reflection of the corrupt heart of man. How anyone would miss this is beyond me.
Others have also liked to point out how the movie "contradicts" the Bible. Yes, there are a few points, but for the most part the reviewers are nitpicking (such as Jephath wasn't Noah's youngest son - but who really cares?!). The "worst" contradiction in the movie (and it's only a contradiction to those Christians who have no understanding of Christian theology) happens twice with the phrase, "In the beginning there was nothing". But clearly this isn't in reference to God not existing (as some reviews have implied), but the cosmos not existing. And since creation ex nihilo is a very Christian doctrine, Christian's shouldn't have any problem with this.
What Noah is then, is a fanciful, imaginative re-telling of the Biblical story which takes the themes of the Biblical source seriously but takes liberties with the story in order to make it exciting and entertaining so that it is almost certainly not what you will expect. It was also kept relatively clean (it is about how evil men are and their destruction, after all). I don't remember any swearing (there could have been some - I don't recall any though), there was no sex/nudity, and the violence was usually less gory than something like Lord of the Rings (e.g. not decapitations - but a few animal guts). There were plenty of oppurtunities to make a rated R film - and the film makers did not.
There are a lot of lessons to be learned in this film and it's a shame that some in the Christian community don't understand even the basics of good story telling. Go into Noah not expecting a rehash of the Bible but a clever reinterpretation of the story that will teach those who will listen. To those who have ears let them hear.