I thought the film was a very good adaptation of the book. However, I felt that the trailer misrepresented the film somewhat, half of the audience in the cinema for the film yesterday seemed to be there thinking it was going to be an American rehash of 28 Days Later. Either that or it was the only choice after Avatar was sold out

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From a critical perspective, very stunning, good cinematography, some beautiful shots (the trailer at "the end of the road" being a good one) and a good use of (lack of) colour. It was like watching the cinematic version of a Post-Apocalyptic piece of art.
Viggo's performance in this is delightfully understated and I felt that the young actor who played the boy was pretty good as well. They were good representations of the characters in the book.
The movie felt more like a good mood piece, instead of showing you scenes of cannibals tearing people apart limb by limb, it concentrated on simple imagery, of what is left behind. I was struck by horror at the human condition with the shots in the house of the pile of shoes, or the stark slash of blood on the snow in another shot. If you had half a brain and thought about the visuals, if you thought about what you were watching, it got it's message across without the sensationalism that the average public neeRAB hammered into their skulls.
It's a clever movie, very understated and bleak.
It's not a Cannibal gore-fest and it's not typical Hollywood Spoonfed fayre, so I don't think it would go down with the average Joe who has just made up their mind to see it on the basis of the trailer. However, if you've read the book, go and see the movie, you wont be disappointed. If you happen to like good cinematography or like atmospheric mood-pieces, also go and see it.
If your cinema viewing of choice is the average Hollywood Blockbuster or Zombie movies, don't bother. It won't be your thing.