Don't believe the hype! This game is a misfire at greatness.
That said the game is not terrible but it misses the mark of great by a wide margin. But here is the big WARNING. Here is what will separate those who like stalker from those that hate it (folks like me that are in middle are likely to be rare), patience. If you are not a patient player, skip this game. You die many cheap deaths. There will be many points of frustration. Its a game for the patient and the old.
Good
1) Large open environments
2) Mix of RPG and FPS
3) Excellent feel and mood.
Bad
1) Most dialog is presented as text. Pre-2000 you could forgive this in a game but in the post 2000 era that lack of production values is not forgivable. It simply breaks the immersion in the game environment to read rather text than hear dialogue.
2) No damage feedback. The only indicator you receive of damage is your health bar on the HUD dropping. Its is a standard in today's FPS that you should get a visual and audio cue that you are being hit. To have to keep glancing at a health bar to know if you have been hit breaks immersion and is clumsy game play.
3) Because all of the colors are washed out an almost everything is a shade of brown, it can be hard to spot enemies from the environment. Also because foe and friend basically wear the same outfits, FF can be hard to avoid.
4) Tilt. The fire fights like any feeling of versicle feel.
5) Russian dialogue. I don't speak Russian and 90% or more of the folks that play this game don't. Not being able to understand what is being said in the ambient environment is very annoying. This should have been an English only option like BF2.
6) Difficult. Sometimes the game can be annoyingly difficult on some of the tasks. To be honest, I play most games on the hardest setting and don't die much. I have been forced to play this game on Veteran and I have died more than the last 3 FPS put together and I have only played the game for a few hours. This wouldn't be annoying if is was the gun fights that were hard but I found myself dying just trying to use my anti-radiation tools to grab a backpack off a crashed truck or retrieve a backpack from a fallen stalker. Some of the radiation zones are little quick to kill your character.
7) Poor inventory system. The inventory system is ripped directly from RPG games. The problem is these same games allow you to pause during the action and do inventory management while not being attacked because the game is paused. This being a FPS that is not possible. You only have two weapon slots so if you find you need a different gun than the two on hand, good luck on hiding behind a truck during the combat to switch. The same if you need other equipment. In a FPS everything needs to be at the touch of an assigned key.
8) No future for MP. The guns are pretty inaccurate as others have mentioned. As a SP this not a big deal because REAL guns are not as accurate as portrayed in most FPS. But for MP, guns needs to be accurate for comp play. At best it might fuel a short lived casual play but the MP has no gas because of the combat engine.