You guys should implement a way for bullets to actually hurt you wherever you get shot. For example, a pistol (lower muzzle velocity) should be able to penetrate through all of your skin layers and depending on the caliber, break your bones. For an assault rifle (higher muzzle velocity) should easily penetrate through your skin and straight through bone.
For an interface, you should have a real skeleton with vital organs, bones, and all the blood vessels (I think that's the proper term for the blood going through your body). If you get shot, the interface will tell you where you got shot from, the entry point, the exit point (if a high caliber rifle), and the damage done to your body. The different points in where you get shot will deteriorate your state. If a bullet breaks your hand, you cannot use your hand therefore crippling your aiming. If you have lost a lot of blood (also forgot to mention to have blood loss according to where the bullet entered and/or exited) the world will lose saturation and you will start to feel dizzy and stumbling. After that, you can pass out or die of a medic doesn't heal you in time.
Another suggestion is that you should have dismemberment. If a grenade manages to get close enough to you and explode, you would lose a limb or two. For example, a mortar shell hits 10m away from you. You will be shocked (slowed down), blurriness, and ringing in the ears. Another explosion happens, you are downed and when you regain consciousness, you lost your legs. This should be in the options menu to disable it or on the higher difficulties (veteran, expert).
Thanks, I would love to see this in the game.