Something along the lines of: You only do damage or you do MORE damage if your crosshairs are actually on the player.
Another thing. As of now, your player is always positioned in the middle of the screen. It would be interesting if you were able to scroll the screen in the direction you are looking, but only as far as your player remanes on screen. Kinda like the way the game Soldat is played. ( www.soldat.com)
I think these two ideas would make the game much more tactical ans skill based. But again, these ideas are just thrown out there just in case someone starts developing this game more.