I realise that everyone else who’s going to has probably already seen it by this point, but I just watched I am Legend at the cinema. Coincidentally, I listened to an abridged reading of the book last week—I’d recorded it off the radio last year—which made it very easy to compare the two.

They aren’t the same story. In fact, about the only thing they have in common is the name of the protagonist and the premise that he’s the last uninfected human being on Earth. And even that’s resolved differently in the two versions.

Some changes, though, were inevitable. The book was written in 1954; half a century on, our understanding of medicine has overtaken it and rendered some of the explanations unbelievable.

Unfortunately, the film gets off to a really poor start. ‘Dr Krippin’? C’mon—have some respect for your audience! And the CGI of the opening product placement car/deer chase is piss poor. The backdrop of New York after the fall of civilisation is convincingly conceived and rendered, but the effect’s entirely ruined by a car that doesn’t appear to obey the laws of physics, nor even to be on top of the road. That kind of thing might be acceptable—cute, even—in an old film like Breakfast at Tiffany’s, but it severely dented my sense of disbelief.

Speaking of CGI, the monsters were also disappointing. Haven’t I seen exactly the same ones in a recent computer game? Actually, the comparison with computer games isn’t quite fair: most computer games have far more convincing physics engines and texture mapping than was in evidence in the film. Another fail.

Apart from that, it’s an entertaining enough film, with some tense moments, but the simple, utilitarian plot is ultimately unsatisfying. Nothing happens that isn’t necessary, which doesn’t help when there are so few characters.

From the book, I missed Robert Neville’s salvation and betrayal by Ruth, and the connection with vampires of folk legend. The film character also gets drunk a whole lot less and is generally far more likeable—and therefore less realistic somehow. On the other hand, I liked the way in which the film introduced us to the intelligence and vengeance of the monsters.

It’s unusual to encounter a film that feels too short these days—many seem to drag on—but I am Legend would have benefited from another half hour of twists. The ending was clichéd, but I didn’t find it entirely objectionable. It’s what we’ve come to expect, I suppose, and the test audiences won’t have it any other way.

Finally, they should have called the film something else. In the book, vampires grow from legend to fact, while humanity in the form of Neville passes into legend. In the film, they listen to Bob Marley. Not quite the same thing.