I also have to express dismay at the low rating this film has on IMDb. It seemed a well done, decently acted movie with a story that is neither ridiculous nor simplistic. I honestly believe it is deserving of an above average rating. Probably what annoyed a lot of people is the poster, which has nothing to do with the movie at all. It is not a film about glorious deaths in violent battles.
The Viking raid on Lindisfarne monastery is a real event that is considered by historians to be the beginning of the so called Viking Age. As with the TV show Vikings, the event is used to inspire the storyline in The Darkest Day, without much concern for historical accuracy, but this film has it a bit closer to reality.
The plot is seen through the eyes of a young monk, one of two escaping from the Lindisfarne's raid and carrying the Lindisfarne's Gospels, a beautifully crafted book that holds "the word of God" and without which the monks believe the Angles country is lost. The book is a real artifact that you can read about. The monks run away from a bunch of Vikings that want the book, believing it holds "the power of the white Christ" and can be used to rule the land. Their escape shows you glimpses of the wild and poor way of living in those times (around 800 AD) in the British Isles. Helped by an old warrior, they meet Christian sectarians and a Pict woman they rescue from bondage and try to fend off the raiders.
I've watched a few Viking related movies lately, something spurned by the TV show Vikings, and this is by far one of the best. It is a low budget English and Welsh film with almost completely unknown actors in a small cast, but they each play their roles well and the bleak and violent trek through ancient England feels realistic and raw. The name of the young monk, Hereward, is an ironic hint of the end of the movie. Again: a clearly above average film, especially if you are in a Viking mood.