STALKER is the prettiest FPS out there. With full dynamic lighting, the exterior environments are wonderful and lively and interior environments are properly run-down and creepy. Two problems here. One, because the game makes extensive use of normal maps, actual variations in the polygons have been foregone. Two, and the reason one is so very noticeable, the game is a giant PC-sucking whore and even my fairly high-end laptop needs to turn off ALL dynamic lighting to run it at any acceptable speed. With dynamic lighting off, the game clips along at 60fps and there is enough detail in textures and models of trees and creatures and vehicles to still look decent. The only problem is, as aforementioned, the low-quality textures and bland models on stuff like walls looks bad.
STALKER is the hardest FPS out there. Particularly early on before high-end armors become more common-place but after enemies start whoring assault rifles. The only problem here is that even on the easiest setting, it may be too hard for lightweight gamers. Compounding the armor problem is the weight-limit. You can only hold 50kg of equipment, including worn armor, without suffering badly. You cannot hold past 60kg period. Your armor typically weighs 5kg, and starts to be useless after a few large encounters so it pays to carry a backup. Weapons all take appropriate ammunition and are varied between NATO and old Warsaw-pact weapons as well as newer designs, which means there's about two dozen types of ammo available in the game, each needing a small selection of guns to be used, forcing you to carry a variety of (heavy) guns. Food is also needed to survive, and more heavily, medical kits.
STALKER is big. It has about a half-dozen each of handgun, shotgun, machinegun, and sniper rifle designs with a few odds and ends (grenades, knives, rocket launchers) thrown in, and unique versions amongst those where only one exists in the game world. It has at least a dozen styles of armor. It has miles of game terrain (although much of it can't actually be walked on, there's still lots of it you'll never explore just because). Which necessarily means it has a whole lot of optional crap available. And especially because item locations, allied, neutral, and enemy creature locations, and related are all random, that means a lot of replay value for unique sidequests (which are, in RPG standard, offered by barkeeps).
STALKER is cool in that it does have an RPGish feel to it. You can take quests given by barkeeps and do them for money, weapons, and artefacts which are practically magical items. Money can be used to buy better weapons or armor, to stock up on food, ammo, bandages, vodka, etc. Gun components can also be removed and moved to less beaten up guns (for instance, silencers and scopes). People who had guns drop those guns when you kill them so it's never hard to get a gun and you can raid corpses for their food and bullets, too. Unfortunately, while you CAN steal everything but the clothes off their back, you CANNOT actually steal their typically higher-level-than-yours armor. Which is another reason the game gets rather hard if you don't follow the treasure-hunting sidequests, many of which lead to high-end armors. Other Stalkers also remember how you've acted in the past. You get a fair amount of aid if you're a nice guy, people shooting at you if you're a bastard. You can join some two of the warring factions as well, supposedly, although I tried and couldn't manage actual membership. Ended up noticing I could already use their shop, bought the best buyable items in the game, and moved on.
STALKER also has a really nice pace and story to it. The story is rather sparse, admittedly, but what there is has a nice grim sci-fi feel I like. The pace, however, is awesome. A fair amount of the game consists of exploring. Sometimes it's relatively peaceful, sometimes it's fraught with danger in the form of difficult-to-spot anomalies and enemies. At one point (and only one point) there was heavy encouragement to use stealth to sneak into a military facility to steal something since the alternative was very deadly. At one point, there was no combat at all where it was very well suited. But most interestingly, whenever the game forces you underground, you can be sure it's going to be creepy as hell. Which makes the above-ground portions into nice breaks from nerve-wracking bits in the depths of the earth, even if the worst fights occur above-ground (typically when the military attacks your position).
STALKER has decided to take an odd take on realism where your gun jams up and isn't perfectly accurate. Furthermore, your gun gets more and more likely to jam and miss shots as it gets more wear-and-tear. Similarly, while your armor may start out being badass, once you shoot a few holes in it, it's no longer quite so good at protecting you. Despite these features, the game also features radioactive artefacts which give effects like making you more resilient to firearms, heat, electricity, radiation, etc. Kind of odd, but since you can choose to equip up to 5, it gives a bit of extra customizability. They also sell well if you don't want them and weigh only about a pound so they're the most weight-efficient items to gather for money, which the plot points out is also the reason most Stalkers are there.
STALKER also has multiple endings. Not sure if I've managed to find them all. But they aren't of the typical 'play the game this way, get this ending' kind of endings, nor meeting a few little flag points. Although that may be part of it; I'm not sure. What I do know is that there are various tiers of endings where you can generally look around the area where one ending is reachable and, if you completed the necessary quests earlier, find openings to whole new dungeons, at the end of which is another ending, which can be foregone for yet another dungeon, and so on. Somewhat unique, that. The area for the final (I think) ending alone had two hidden pieces of top-end armor, which is exceptionally high for this game, largely because the enemies themselves were rediculously overpowered.