If you're a Fallout fan or a F.E.A.R fan, or both, this game is your keeper.
For some reason, since the Fallout series, gamers dig nuclear-wasted lands which sort of is the ultimate modern explorer's paradise to the unknown. You would have monsters that are actually mutated animals, and then human enemies that are faction-aligned or fanatics of an unknown cult. With radiation, anything is possible and explainable. In Stalker, an interesting addition to the wasteland would be the phenomenon called anomalies, which serves as traps, both to you and your enemies alike.
I would like to compliment the A.I. which is sort of similar to F.E.A.R where they use strafing and flanking tactics, which makes the Stalker world so real and so damn hard too. The game's hard man, and reloads are frequent, but satisfying given the loot. What amazes me in the realism factor is that your bullets have real-world projectile physics too. Yes I mean the bullets do droop down after some distance, like the Crossbow in Half-life 2. Creepy.
On the other hand, what I find crappy is the unnecessary long distances between locations and the unlimited enemy respawns and to some extent, the limited number of merchants, which makes back-tracking a CHORE. Also, you need patches for this game, the original version is glitchy. Other than that, it's a nice contender for a Fallout fan like me.
KingLim