Darren Arnofsky is incredibly talented, and I make a point of seeing his movies. Despite a theme that didn't appeal to me, I made sure to see it in the theater.
Arnofsky's achilles heel is his tendency to get stuck in his head, and Noah is definitely that kind of movie, like The Fountain, or the worst parts of Pi. Noah is ambitious. It's got a very healthy special effects budget, and spends a ton of effort on costuming and makeup. On the squishier parts of the movie, it's got a script that is trying very hard to reinterpret a foundational myth, and a melodramatic acting and directing style that is quite obviously intentional.
The aforementioned melodrama makes it very clear that Arnofsky feels very strongly about...something. But what, exactly, is Noah ambitiously trying for? The Bible has a lot of cultural cachet and baggage. Noah could be an unedited retelling, an environmental stewardship parable, a dissertation on myth, or a simple rejection of the story. Arnofsky refuses to take any of these options, settling on something that's unclear.
The closest framework is character study. Noah deals constantly with trying to interpret the metaphors and messages of a distant God; in this way he's reminiscent more of Abraham or Job than the traditional cultural portrayal of outcast-cum-steward. Perhaps Arnofsky read The Origins of Consciousness in the Bicameral Mind and took it a bit over-the-top?
Whatever Arnofsky wanted the movie to be, it ends up a mealy-mouthed mess. It seems so determined to strike out on its own that it rejects everything that's interesting about Noah as source material. It's a lot like The Fountain, in fact, and there's really no reason to see either one.