A review from The Movie Snob:

A Very Long Engagement (B). This is an anti-war movie disguised as a romance. The year is 1920, and even though World War I is over, provincial French girl Mathilde (Audrey Tautou, Amelie) refuses to accept that her fiance, Manech, was killed at the front in 1917. It was reported that he was executed along with four other French soldiers (for the crime of deliberately shooting themselves in hopes of getting sent home), but Mathilde holds out hope that somehow he survived, and she embarks on a quest to find out the truth. A great deal of the movie is told in flashback, and the director vividly depicts the horrors of WWI's trench warfare and the casual brutality of the men in command each time Mathilde's investigation turns up new facts. Not a bad movie, although a little long for my taste.