A taste dependant game you'll either play or not.
Stalker's main selling point was and is the "living world", what you do can and does affect the world around, BUT the world around you doesn't really need you... If you just stood in a room for 2 hours then other Stalkers would go on with business as normal, animals would move around, and not like Oblivion which made all it's NPCs follow prescripted paths, but dynamically.
The game is set in 2008, 19 years after the second Chernobyl meltdown (the fiction of the game is based upon the fiction of a second meltdown) and manages a very good post-apocalyptic feel and style, weaponry is based on real life, and so are the various wrecks and buildings in the game.
The combat is what will make most people love or hate the game, it is extremely realistic, requiring duck and cover tactics, and ammo isn't just lying around either (like most FPSs) so you have to conserve it carefully.There is also bleeding, which has to be staunched by bandages.
The stealth portion of the game is also well done, the AI vision is well depicted (you can hide behind bushes, etc) and the "noise bar" on the left side of the screen helps in avoiding detection since you know when you're making too much noise.
Two interesting parts of the game are anomalies and artiacts, anomalies are - well - anomalies which can harm you in a variety of ways if you go near them, but the reward for successfully avoiding an anomaly can ba an artifact, which can be traded or used to modify your statistics.
Since the game takes place in a nuclear meltdown zone there is of course radiation, the method used to cure radiation poisoning is a bottle of Vodka, or in more serious cases anti-radiation injections, and if you get caught in radiation withiut one of those you ARE in trouble.
Overall Stalker manages it's goal - to be a freeform, open ended FPS/RPG -very well, but the combat system might be a bit off-putting to some and in other cases you might just not like the game for no reason other than it doesn't appeal to you.