This is one of the few FPSs where I almost never engage NPCs without solid cover and trigger discipline, and sometimes just don't engage at all. It's exactly what I want from an FPS game.
If you shoot at an NPC in STALKER (especially if you play it proper...on hardest difficulty), you're in for an intense firefight, and if you aren't prepared, and that NPC has friends, you'll probably lose. I played through Misery on CoP at the hardest difficulty, and there has never been an FPS that made really consider firing a bullet like that.

It's the antithesis of the Western philosophy of "I'm a badass" game design.
In STALKER, you're
nobody. The Zone doesn't need you. You're not a badass, or a superhero. You're a human being in desperation. Desperation is lacking from modern gaming.