Trashing New York is an LA tradition. Since King Kong first climbed the Empire State Building in 1933, Hollywood has been biting into the Big Apple more regularly than Al-Qaeda. Its modus operandi have ranged from the great gorilla to the great apes (Planet of the Apes (1968)), a giant lizard (Godzilla (1998)), the Atlantic Ocean (Artificial Intelligence: AI (2001)), a new ice age (The Day After Tomorrow (2004)) and of course, aliens (Independence Day (1996)). And this holiday season it’s done it again – I Am Legend showcases NYC as a survivalists’ playground, reclaimed by nature and besieged by marauding zombies.

Based on Richard Matheson’s 1954 pulp novel – incarnated twice before on celluloid as The Last Man on Earth (1964) with Vincent Price and The Omega Man (1971) with Charlton Heston - the apocalypse scenario is also reminiscent of Brit flick 28 Days Later… (2002). But this time there’s Will Smith and a huge budget. The 2007 version opens with Emma Thompson in an un-credited cameo. She plays the amusingly named Dr Krippen, a scientist who has cured cancer. The only problem is, her cure is viral, and as any good scientist and all good screenwriters know, viruses mutate - into zombies.

Cut to 2012, Times Square, gone all Tarzan – there are vines, deer, lions… a conspicuous lack of people and some large biohazard symbols. The scene is impressively created and there’s something endlessly fascinating in seeing monolithic NYC transformed. Will Smith is Robert Neville, the only living boy in New York - who’s handily a US military scientist. Immune to the virus that’s wiped out most of humanity and turned the rest into light-sensitive monsters, Neville dedicates himself to curing the cure for cancer.

What’s curious about this film is that it’s been a huge pre-Christmas hit, topping out the American box office, yet it’s as bleak as a turkey’s December horoscope. For the first half, director Francis Lawrence has stripped away at the horror and sci-fi elements dominant in previous tellings, to reveal the drama of a man forced to survive alone in a world seemingly without God. It’s like an existentialist indie picture…with lots of CGI. By day Neville hunts the wildlife running down Fifth Avenue, practises golf shots off the back off an aircraft carrier on the Hudson River and visits a store where he’s set up mannequins in place of people. He borrows DVDs and then returns them, maintaining social norms and circling the wagons against anarchy. For over two years his dog Sam has been his only living company. Between Smith’s performance, Lawrence’s direction and production designer Naomi Shohan’s vision, the first half of this film has the confidence to be detailed yet grand, emotional but not sentimental and slow though tense – very, very tense – despite the fact it’s essentially the narrative of one man and his dog.

But this tale of humanity’s second fall starts to fall apart when the symbolism gets overtly Christian and the plot expands beyond Neville and into Pilgrim Fathers territory. Neville had lost his faith in face of the virus, but the narrative turns when he meets a girl who believes she is a messenger from God. Rosaries and white chapels ensue and everything gets clouded in some fuzzy theology that throws away the film’s earlier, ambivalent promise. Ultimately neither the CGI monsters (why not use actors?) nor the happy-ending are convincing. This is an entertaining film with a moving performance from Smith, but sadly its denouement sacrifices thought in favour of plot – and the plot isn’t as good as 28 Days Later….