I also hated the trailer. Soldiers leaping out of trenches and running onto grass.
However, when you actually see the film you get the context. The long established static lines, which the two protagonists advance through during much of the of the film show the realism (or what I have always considered it to have been) of trench warfare. The more forward lines in the later part of the film, which have been recently dug due to the Germans' resetting of their defensive line, allowed me to change my view of the trailer's authenticity.