Note: This review has been slightly edited.
I had difficulty choosing either 'Innovative' or 'Immersive' or 'masterpiece' to put as a bottom line above me, but because this game is very immersive, but even includes a lot of new things to the genre, I chose 'Innovative', but it still sure is immersive and inevitably a masterpiece. It is on par with games like Half-Life.
GSC Gameworld has made old RTS games about the Cossacks, but they were not so successful and recieved little recognition. Then they turned to making their first major FPS. Incredibly, just because of one game, GSC Game World has become one of my few favourite gaming developers. This sets a new standard miles away from the standards of other FPS's released at the same time.
I read a PC gamer magazine that held the best (and sometimes worst) shooters of 2007 (e.g Best Third-Person-Shooter: Gears of War, Most innovative: Portal) according to one pretty clever guy. Call of Duty 4 was ranked the most overrated shooter of 2007 for its enjoyable, but incredibly linear and scripted campaign and basic gameplay. STALKER was ranked the most underrated shooter for the non-linear game world (quite the opposite of CoD4). Gaming-related, it made me feel much better than I have been for a long time because it was about time someone shoved factual criticism down Infinity Ward's throat. Making huge profit doesn't make a game good. IMO, the industry is in much need of titles with good replay value that feel very atmospheric and immersive. STALKER has all that.
This game is NOT for FPS-newbies. Your chances of survival at times are only slightly better than in real-life. Playing this game on novice difficulty (easiest) is like playing CoD4 on hardened (and sometimes on veteran). You have about as much chance surviving out in the open as in rainbow six vegas. The enemy is intelligent and will ambush you at times. You do not absorb a lot of bullets before death so if you do not have medpacks or bandages along with good armor, you're screwed. However, it is not impossible to complete and I did find it easier than RPGs like Fallout 2. If you played a lot of FPS's like me, you will have less difficulty than most people would especially if you can find good armour suits in the game.
The action is not as intense as games like Crysis or Half Life 2, but it has the most realistic feel I have ever experienced. It is more slow-paced but very innovative itself. Triumphantely, GSC's most recognised FPS turns out to be one of the most realistic in terms of feeling and GSC are not veterans of FPS's like Ubisoft or Treyarch.
The gameplay is so open and non-scripted. You are a S.T.A.L.K.E.R in Chernobyl, a place filled with other stalkers and with bandits, soldiers and dreadful mutants. This is a survival game as well since you occasionally must have food to stay alive and you require bandages to stop bleeding if medkit does not work. Amusingly enough, if you don't have vaccinations to help you when you are affected by radiation, drink vodka which will reduce it's effects, but also make your character drunk and dizzy. This is a game where everything is really up to you. There are small RPG elements, but this is not an RPG, and the game is better than Oblivion. Since the gameplay tries to be realistic, you'd think there is nothing so intelligent or unique, but the truth is there is. You would not expect this, but your guns can jam in combat so you would need to reload and fix them. I don't think guns have ever jammed in a video game before this so I must say, well done to realism.
The ambient gives you the most atmospheric feel ever seen in a video game. You really feel like you are in Chernobyl, so that keeps you far more on the edge of your seat if you hear something and all you see is objects floating in the air then flying at you when you are in underground labs. You will see real life places along with some (personally assumed) fictional ones like Yantar. But it is not just the ambient and perfectly haunting music that can creep you out, but also your surroundings. The game only features little blood splatter in combat so despite good ragdoll effects the game is not that violent like the 'M' rating suggests (and that ugly, creepy guy on the game cover does not even exist in the game), but to make up for it, the developers use your environmental surroundings for gore. You will come across decapitated body parts (which are meant to be there as part of the game) and deteriorated bodies and other graphic stuff and the context which they are portraying always gives you the feeling that you will be entering a dodgy place, and the battle that was fought there was no coincidence.
Dialogue options are small, but you really feel like you are actually talking to someone when you hear how they react to your dialogue choices. You will see some stalkers sitting at a campfire and you can listen to one play guitar. So much happens in real time. Bodies of the people you killed, or others killed, remain in the area for a long time. Want to satisfy the loneliness of the mutant dogs or pigs in the fields, drag the body to their location. I must be boring you with giving away so many awesome gameplay features so I will move on.
Graphically, it is actually very good. Cracks on concrete don't look like they're drawn, but actually are modeled well enough to look real. Lighting is faint when outdoors, but that makes a cloudy day in the day/night cycle really feel like a real-life cloudy day, and sunsets/rises look beautiful, and many objects have amazing detail. Exploring the labs and other places is creepy, but still enjoyable. The visuals are not revolutionary and are a tiny bit dated, but I think people need to understand some things. The game was scheduled to be released in 2003, but was delayed quite often and it would not have run on computers these days and if it did, it would be pretty damn buggy and glitchy and slow, and the bugs that some people experience these days would only be a fraction compared with that time, so of course they may seem a bit dated in some areas. And yet the graphics are even better than Half Life 2's and Half Life 2 came in 2004. Therefore we still need to credit GSC, because they could nearly have managed to create graphics that almost could have been released earlier than HL2 and outrank it.
Main story is a bit brief and like other critics say: A bit incoherent. It uses an orthodox plot of a character suffering amnesia and trying to solve the mystery behind it. But it is still a well done tale, and makes me interested in seeing the movie that inspired this game's setting. STALKER's main missions (the ones you choose to do to follow the main story) are very well designed both in environment and objectives. It starts out with simply raiding bandit camps but eventually you have missions like one when you are tasked to simply finding a key to an underground lab and once you're in, you must find the codes to unlock doors to proceed. It may sound simple, but the fact that there are ideas which are very rare in games, this is pretty well done, and considering how is not often that you would find missions that are well designed objective-wise, plus are not even repetitive.
The game's side quests, although very simple and predictable, are also not too repetetive and all your options and the well thought-out different endings (2 of which are beautifully visualised), and the well-designed main missions gives you some of the largest replay value I have ever seen. You won't get bored since you don't often repeat the same thing (in main missions at least). This is truly a game that's large as life itself, with a convincingly grim image of one of the worst man-made disasters while still being enjoyable. Fallout 3 is another amazing game, but it does not have an atmosphere that keeps you interested and stays with you forever like S.T.A.L.K.E.R, plus it is not as intense. A lot of modern games are great, but are too staged and with between little to no choices, so just go for this game (Or Fallout 3. It is still very good). If you have a good PC, you should have little problems with bugs.