Someone in /r/totalwar had the idea of a TW game going up until 1900, and while I was pretty sure warfare in the late 19th century wouldn't support a TW game, I couldn't put the reasoning into words because I honestly didn't know. During WWI, battles were mainly fights between large numbers of infantry attempting to outflank each other or simply outgun each other with the support of massive amounts of artillery. During the Napoleonic Wars set-piece battles were still fought where generals threw their armies at each other and attempted to win tactical advantages over their enemies utilizing the strengths of their army composition. First off, am I correct in that identification of differences between the styles of tactical warfare or am I completely wrong in my thinking and are there other things that set the wars apart in that aspect, and as to the original question: when were battles more like the former than the latter?
That's actually what they did initially. For the first phase of the war until about the First Battle of the Marne, the more traditional modes of warfare, the broad charges and the cavalry assaults were used. Trench warfare began when both sides realized that the development of new technology meant that deeper fortifications (trenches) were needed.
Even up till the Franco Prussian War of 1870 Napoleonic tactics were still effective. In this war as well, both sides had breach loading firearms and advanced artillery. I think the biggest problem for a TW game however, is not the power of the weaponry, but the sheer number of troops involved. In almost every single TW game, the amount of troops simulated on the battlefield has been much much lower than what an accurate battle would have involved.