I was about to complain about how headshots don't reward you more so why not just go for bodyshots, but then I realized that they do by looking at the points, and it surprised me even more when I realized that there's even hat shots on top of that. So I guess a simple solution to that would be to add "Bodyshot! +100" like pop up texts when you score. Thus, even if the player didn't get a headshot, they would've noticed that there might be one and proceeds on playing to get it.
Adding progressing difficulty would be nice, or maybe there just happens to be one and I didn't notice, but I enjoyed this the way it already is on hard mode, so I wouldn't complain.