I've been clearing the facility under Red Forest for at least ten minutes now, and I haven't seen anything. I could just charge in mob-handed and trust to firepower and reflexes to save me from whatever's lurking here, but instead I've been creeping slowly and quietly through the abandoned lab, sweeping each room in turn with my suppressed VAL. This is the beauty of a good game: you create your own dramatic tension.
Then, after what must have been a kilometre or so of taut, silent infiltration, I come into a generator room slightly larger than the chambers before, and see something dark and not entirely human squatting half-hidden behind a pillar. It's a bloodsucker, one of the more dangerous mutants in the Zone of Alienation. I've killed bloodsuckers before, but it's always a fight, and as soon as the mutant is aware of me it'll cloak and sprint from cover to cover, erratic and almost invisible, until it's right on top of me.
I look at the awareness bar. It's jerking up, heartbeat by heartbeat. In a second or two, the bloodsucker will be aware of me. And, holding my breath, sitting frozen in my seat as if the thing might hear me through the screen, I reach up, switch my VAL to full auto, and savour the last second before hell.