The war in 1918 wasn't just shelling and gas. It was a war where small unit combined tactics had been learnt the hard way and developed by all armies. At the level CM simulates even mid war battles would be reasonably interesting - by 1916 the French had developed the move and fire and the British quickly adopted it. It would be no different really to a company size bocage fight. Gas wasn't an effective weapon - initally it had shock value but armies soon developed defences against it. It would mainly add to the fog of war. This is the problem with a WW1 game - everyone assumes its just shelling, gas, walking slowly towards a dug in MG post and waving a walking stick at the them.