Having read all the other reviews, I think that most of them are rather unkind to this movie.
Prior to the battle, the Somme area was a quiet backwater of the Great War with activity consisting of both sides daily lobbing a few shells into "No Man's Land" just to maintain the pretence that there was a war on. Neither side wanted to do anything but have a quiet life.
As for the soldiers being too clean, well in a non-combat area, baths and showers were available as was clean clothing.
The Somme area is chalk, so there would have been none of the mud usually associated with trench warfare.
I'm old enough to have had conversations with Great War veterans, like my grandfathers and other relatives and their perception of the war was of
99% total boredom and 1% sheer terror.
I enjoyed the movie, despite being a Great War buff. The weapons were correct, the uniforms correct. As for the movie, well scripted and well acted.
Worth the money. Buy and enjoy