This game is probably the weakest in the franchise.
For starters, its quite linear compared to the other 2. There's no central hub and it feels like you are just going from point A to point B.
The faction war system is interesting, but its poorly executed and is quite buggy. Enemy spawn rates are absurdly high, and the devs decided to program mutants to attack bases as well. Nothing is more frustrating than wiping out an enemy main base, only for mutants to kill the garrison when you aren't looking, resulting in the enemies repopulating the base again. Its even worse when the mutants wipe out your faction's base, meaning that you have to run all the way back, kill the mutants, and wait for the AI to send friendly NPCs to repop it. And that's assuming the AI didn't break and is working as intended.
The combat in vanilla is also pretty jank, as the devs decided to make guns have a random chance of dealing no damage, which means that even it would take only 2 shots to kill a bandit, you might end up spending a clip. And the AI doesn't suffer from this mechanic.
You don't even eat now, which is a pity because that was a neat mechanic in SoC, and I'm happy they brought it back in Call of Pripyat.

Now, you might be wondering why I'm recommending this with all of these terrible features.
Well, for 2 simple reasons - Mods, and legacy

Mods improve the game considerably, fixing all of the terrible design choices the devs made. SRP is basically an unofficial patch and it even comes with a feature to make the guns work properly.
Probably the only mod you'll need, really.
It might sound odd to recommend a game based on available mods, but with the Stalker series you pretty much need a couple of bug fix mods to make it stable or to iron out some of the more poorly implemented features. You don't really need more than that, imo.

By legacy, I mean that whilst the game does get a bunch of things wrong, it does add some new features to try to mix things up and make the zone feel alive and dangerous, and it can be pretty fun once you get your bearings.

For starters, there are now Emissions. Most people seem to hate Emissions, but I like them; it provides a sense of danger and gives you a better impression of what makes the zone so dangerous, that at any moment all hell will break loose, and the only thing you can do is hide and wait for it to end.
For anyone not familiar with the stalker series - an Emission is when the Chernobyl Nuclear Power Plant suddenly releases a massive burst of psychic and radioactive energy, killing anything that's out in the open in the Zone. The only way to survive is to find a nice solid bit of shelter and hope it holds.

You can now upgrade and repair weapons, which is a nice change from Shadow of Chernobyl, where you had to ditch a weapon or suit because it got too badly damaged. As of Clear Sky, if you like a weapon or piece of armor you can stick with it, which opens up some Role Playing options.
One of the more interesting mechanics it introduced is the ability to detect in hunt artifacts; instead of lying out in the open like in SoC, you now have to look for the damned things with a detector. Again, this adds to the atmosphere of the Zone, and provides a bit of tension to artifact hunting, as sometimes you will have to go deep into an anomoly field before the artifact spawns.

All of these features would later be implemented in Call of Pripyat, so I would argue that its worth getting Clear Sky just to see the evolution of the Stalker series. If you are a fan, that is.
Just be sure to mod the hell out of it, and take a lot of health kits for that damned machine gun nest in the Cordon.

All in all, its a good game. It has its problems, but they can be easily solved, and the game can be quite fun despite of them, as the core stalker mechanics are there still and are pretty solid.

This game is probably the weakest in the franchise. For starters, its quite linear compared to the other 2. There's no central hub and it feels like you are just going from point A to point B. The faction war system is interesting, but its poorly executed and is quite buggy. Enemy spawn rates are absurdly high, and the devs decided to program mutants to attack bases as well. Nothing is more frustrating than wiping out an enemy main base, only for mutants to kill the garrison when you aren't looking, resulting in the enemies repopulating the base again. Its even worse when the mutants wipe out your faction's base, meaning that you have to run all the way back, kill the mutants, and wait for the AI to send friendly NPCs to repop it. And that's assuming the AI didn't break and is working as intended. The combat in vanilla is also pretty jank, as the devs decided to make guns have a random chance of dealing no damage, which means that even it would take only 2 shots to kill a bandit, you might end up spending a clip. And the AI doesn't suffer from this mechanic. You don't even eat now, which is a pity because that was a neat mechanic in SoC, and I'm happy they brought it back in Call of Pripyat. Now, you might be wondering why I'm recommending this with all of these terrible features. Well, for 2 simple reasons - Mods, and legacy Mods improve the game considerably, fixing all of the terrible design choices the devs made. SRP is basically an unofficial patch and it even comes with a feature to make the guns work properly. Probably the only mod you'll need, really. It might sound odd to recommend a game based on available mods, but with the Stalker series you pretty much need a couple of bug fix mods to make it stable or to iron out some of the more poorly implemented features. You don't really need more than that, imo. By legacy, I mean that whilst the game does get a bunch of things wrong, it does add some new features to try to mix things up and make the zone feel alive and dangerous, and it can be pretty fun once you get your bearings. For starters, there are now Emissions. Most people seem to hate Emissions, but I like them; it provides a sense of danger and gives you a better impression of what makes the zone so dangerous, that at any moment all hell will break loose, and the only thing you can do is hide and wait for it to end. For anyone not familiar with the stalker series - an Emission is when the Chernobyl Nuclear Power Plant suddenly releases a massive burst of psychic and radioactive energy, killing anything that's out in the open in the Zone. The only way to survive is to find a nice solid bit of shelter and hope it holds. You can now upgrade and repair weapons, which is a nice change from Shadow of Chernobyl, where you had to ditch a weapon or suit because it got too badly damaged. As of Clear Sky, if you like a weapon or piece of armor you can stick with it, which opens up some Role Playing options. One of the more interesting mechanics it introduced is the ability to detect in hunt artifacts; instead of lying out in the open like in SoC, you now have to look for the damned things with a detector. Again, this adds to the atmosphere of the Zone, and provides a bit of tension to artifact hunting, as sometimes you will have to go deep into an anomoly field before the artifact spawns. All of these features would later be implemented in Call of Pripyat, so I would argue that its worth getting Clear Sky just to see the evolution of the Stalker series. If you are a fan, that is. Just be sure to mod the hell out of it, and take a lot of health kits for that damned machine gun nest in the Cordon. All in all, its a good game. It has its problems, but they can be easily solved, and the game can be quite fun despite of them, as the core stalker mechanics are there still and are pretty solid.