I was always puzzled by Guernica. It looks so ugly (I think most people who saw it for the first time and didn't know it was a famous painting by Picasso would agree), so how did it get so famous in the first place? Perhaps the point was that war is ugly, so the painting also had to be ugly? But it looks literally like a bad children's drawing. Maybe it got famous because a famous painter making an ugly painting on a serious subject was a novel and unconventional idea.