This was a book written by a WWI veteran, so even though the story is fiction, many of the small details are correct with what he saw and experienced. The original movie from 1930 is very good. One of the greatest war movies ever made, possibly the greatest. I assume you are asking about the recent one that was made, I have not seen the new one but I assume the story is mostly the same.
Similar ones that are also good are They Shall Not Grow Old, which is more of a documentary that is all taken from writings that WWI veterans wrote about their own experiences in the war, and showing actual pictures and videos taken during the war. Some videos of battlefields show real soldiers who have died because it is all real recordings, so some of this doesn't feel good to see. But it's interesting showing how these men actually lived every day in the trenches. Details like the Brittish men draining the hot water out of the barrel cooling jacket of their Maxim machine guns and using the hot water to make tea.
Lawrence of Arabia is also very interesting, made in 1962. This is based on a real story about a real man. Showing how these middle eastern countries were affected and changed during and soon after WWI. There must be some details that are wrong, but overall it is mostly a true story which makes it more interesting. This movie is also very long, and boring in some parts. I watched it from a file on my computer and was able to watch it at double the regular speed, and it was more enjoyable this way.
The Battle of Algiers from 1966 is also one of the most accurate war movies ever made. About Algeria, and the conflicts between the French and the Algerians. Everything shown in this movie are from real events and real things that the French and Algerians did to each other, and it shows a very accurate view of how this conflict accelerated. It shows the crimes done by both sides, which is uncommon because most films try to cover it up and try to make one side look bad and make the other side look good.
