As a military historian, I can tell you that this is a totally credible, beautifully crafted, brilliantly acted WW I war movie. The trench settings, No Man's Land and the ruins of the French towns and villages on the battlefield are as close to how they would have been during the war as possible. Most importantly, the main actors as well as the supporting cast do a hugely credible job of representing life as it was under battle conditions on the Western Front in the Great War.
The action scenes are brilliantly filmed and presented. Totally believable. There is no gratuitous violence for violence sake. When such action(s) occurs, it is all part of the story. When the battle scenes take place, individually or in the form of a large assault as near the end of the film, the presentation is superb and authentic.