Like a noise or graphic every time you hit someone, one in same the vein as Team Fortress 2 or Modern Warfare. Don't tell me its absence is meant to heighten the whole immersion aspect of the game either, cuz you can see if you kill someone the Tab window or the kill log. This would be enough if the kill log wasn't so oppressively big.
If there's one thing those AAA, "casual" games do right, it's accessibility and user experience