Darren Aronofsky has apparently been obsessed with Noah since he was a teenager. Watching Noah, that makes a lot of sense – this is the sort of movie a teenager concocts in religion class, half-listening to Biblical tales while thumbing a post-apocalyptic fantasy novel. The film has more in common with the film adaptations of The Road and Lord of the Rings than a Biblical epic in its first half, Noah (Russell Crowe) searching for salvation in a grey wasteland that features both magic and “fallen angels” in the form of CGI rock monsters.

Noah’s first half is weird and ambitious and, well, not very good. It’s fantastical and absurd – he builds the arc after visiting his grandfather Methuselah (Anthony Hopkins), who gives him a magic bean to grow a forest out of nothing. There are scraps of characterisation – his eldest son’s lover, Ila (Emma Watson) stresses that she can’t bear children, his second son (Logan Lerman) wants to get some lovin’ before the rains come – but it’s all washed away by an emphasis on special effects and a confrontation between Noah and generic bad guy Tubal-cain (Ray Winstone). Aronofsky is usually notable for his visual flair, but he seems to be stuck in blockbuster mode here; the fact that the visual effects look like a film from a decade ago doesn’t help.

An hour or so into the proceedings, the heavens open up, the Ark takes to the sea and you start to get a sense for what Aronfosky was trying to achieve. Two of the film’s most memorable moments fall in the middle of the film. In the first, an outcrop littered with wailing, desperate individuals has wave after wave crashed against it, Noah steadfastly refusing to come to their aid. The second is Noah’s grim recounting of the creation story – part Bible, part Big Bang – with humanity positioned as the cause of all the world’s woes.

At this stage, the film takes a moment to consider the immense weight resting on Noah’s shoulders. This is a man not only tasked with salvation, but to observe and participate in the destruction of humanity, to essentially be an unfeeling bystander in the face of his species’ devastation. It’s a compelling idea, and Crowe sells the hell out of it, playing another twist on Aronfosky’s favourite formula (protagonist becomes consumed by an obsession/addiction until it strips them down to the darkness at their core).

It’s not entirely ineffective – there are some moments where raw emotion cuts through the artifice – but injecting this kind of realism into the picture is a lost cause after the cartoonishness of the first half. Not to mention trying to take Noah’s story completely seriously forces you to put some thought into the specifics of repopulation. In other words, a whole lotta incest.

You have to admire the chutzpah behind Noah. This is a film very loosely based on the Bible that spends half its time with rock monsters fending off an army and the other half examining the dark tendencies of the human soul. The fact that this kind of film exists at all – let alone with such a large budget and marketing push behind it – is sort of a miracle. That miracle, unfortunately, doesn’t keep Noah from being an uneven mess; admirable but deeply flawed.