How about pain skins? You know, peoples clothes get blood stained and such, and you can conduct a little triage if your on their team so you know who to back up and who to let die. (If you really though I was gunna say let the dying guy live and leave the living guy on his own... ugh.) Also, instead of somebody's head flying off when you get a headshot (which is pretty messed up, that would have to be a helluva strong bullet,) a nice puff of blood ejects from the opposite side of their head and they crumple in that direction, the proud bearer of a new hole in their head (I NEED A HOLE IN THE HEAD LIKE I NEED A HOLE IN THE HEAD... whatever.) Another cool thing would be to shoot the weapon out of their hand. Shooting the weapon may not do it, but shooting their hand bang on will definitely make somebody drop the weapon.