War is gruesome either way, but the warfare of WW1 (or at least, the most famous parts of it), were famously gruesome. It should be noticed that after the first World War there began a huge anti-war sentiment due to this. The treaty of Versailles rendered the whole thing absolutely worthless.
WW2, for the victors at least, ended on a high note. The invasion was succesful, as were the bombings of Germany and Japan. War was great, war was succesful. There was an important human rights movement, but pacifism had to wait till Vietnam.
Just compare it on google images, notice the heroics and exciting action for WW2 and the dullness and dirtiness of WW1:
WW1
WW2