I've always looked at WW1 as the Soldier's war, and WW2 being the civilian's war. It was like the suffering of those poor bastards in the trenches just wasn't a strong enough message and so the world needed to have those horrors put upon the everyone. It's all well and good to be sending your brave boys to go fight in France to do right by king & country, but a whole other thing to having your homes bombed, being under siege so long that you eat your children and neighbors, and watch a country nearly bleed itself to death by throwing unarmed bodies at mechanical monsters en-masse just to buy time.
But, on the soldier's side, 2 was familiar enough due to the recency of the previous war and the possible horrors were known, whereas 1 was something entirely new and such a dramatic shift from the way war had been conducted throughout history. Those brave boys had no idea what they were getting into, with only the glories of Napoleon/Wellington and brief Franco-Prussian wars to give them an idea.The world was so shocked in what was happening that it literally had no idea on how to end something that was clearly well beyond he scope of intent.
They're both interesting and fascinating in their own ways, and I think comparing them is very much an apple vs oranges scenario.