Nothing humbles a fan of first-person shooters faster than a hardcore Mil-Sim like Hell Let Loose: Vietnam.
Picture it. You're creeping under cover of the jungle canopy as helicopters whir overhead. Short sharp shocks of gunfire are your only real guide towards a forming frontline; squad orders are the other, as the voice of a squadron Commander crackles over the comms line to scramble Infantry units back through dense brush to reform fracturing formations. As enemies pour over the crest of a distant hill, your M16 rumbles as bodies crumble. And then, nothing. A bullet fired from an unknown location rips through your torso. Medics in the area ignore your pleas for help. The long walk back to the action begins again.