There should be an Extreme HardCore mode. Instead of regenerating health, your screen stays red and maybe you even limp a bit. And also, the guns can jam so you have to reload again. And there would be absolutely no HUD elements, even no indication of who killed who and who got the bomb and you cannot press TAB. And maybe you would also have a fear level. If you are in the heat of action, your movements become shakier and more anxious and therefore more difficult to aim.

And meybe you'll even need to eat and drink in the game if you camp lol. (nah that's just too much.)