It is tempting to compare Centurion to Ridley Scott's "Gladiator", but other than the fact that both movies deal with Roman soldiers,they have very little in common.
Where Scott's "Gladiator" is a broad tale with a larger than life hero who comes to shake the entire Roman Empire, "Centurion" is much more restrained, less presumptuous, and more focused on telling one small story very well.
"Centurion" is set in Scotland during the reign of Hadrian, who would eventually order the famous "Hadrian's Wall" to be erected across the northern boundary of Britain to keep the Scottish Picts out of Britain. "Centurion" is the story of some Roman soldiers running for their life from the Picts near the end of Rome's time trying to subjugate the Picts.
The landscape in the movie is gorgeous, though I suspect it was shot farther north (in the Scottish Highlands) than the action in this movie was really meant to take place (a bit more to the south, closer to the English border). This is a pure adventure movie, with no illusions of telling a grander story (as in Gladiator). The action, the acting, the directing, are all very good and very gripping. The story is so simple and so well told that you'll be hooked quickly, and barely move in your seat for the hour and a half that the movie runs.