Truly meh.
I find that this is a good concept, executed poorly. Unlike the others though, I'm not just going to write "boring boring boring". The game got too repetitive too fast. I got to level 10 and realized I was still doing the same thing: aiming my shots so that it would curve a certain way against a wall to hit a stationary person. I decided to check out the level editor and found that the only objects were 'People to kill' and the boxes, nothing else.
You could've expanded the gameplay by adding things like moving platforms or walking bad guys or anything to keep it interesting, not just challenging, or rather interestingly challenging. Challenging in the sense that I want to keep playing the game.
7/10