There are times where Clear Sky is absolute genius. Unfortunately, there are others where the game is, at best, broken.
Clear Sky is a bit conflicting in terms of its quality. As a sequel (or prequel in this case), it brings several improvements to the original. The new artifact system is genius. Instead of waltzing through the Zone casually observing hopping rocks, you now are forced to hunt for them. Because they are invisible, you, the player, must throw yourself in harm's way for the chance of obtaining one. This is a much greater risk/reward relationship than in the original.
The upgrade system is also a vast improvement as well. Your guns and your suits suck unless you upgrade them. And the system is made in such a way where you cannot choose all the available upgrades. Choosing one upgrade nullifies another. This forces the player to weigh the advantages and disadvantages of each upgrade. It is engaging, and it is a rewarding system. The upgrading system gives you a great reason to make money and not race through the game.
Just as it has its great moments, Clear Sky also has its weak ones. At best, both the emission and the faction systems are totally and completely broken. Emissions are said to be random, but they aren't. In fact, when you reach a certain part of the game, emissions happen every single time you load from an autosave. They generally only happen when you load a level. And they never ever happen mid mission. This completely ruins the emission system that I loved in the modded version of the original.
The faction system is useless because you cannot eliminate entire factions. They keep respawning. And there's nothing you can do to stop it. So, unless you want to waste tons of ammo and make yourself enemies with powerful, well armored people; joining a faction is completely useless. Yes, you gain a base and some cool equipment. But without the ability to eliminate factions, a faction system is useless. There needs to be a decision and consequence system. Like, for example, a system where if you eliminate, say, the Duty; then the Zone gets littered with bandits and mutants. That's what a faction system should look like. The ability to totally destroy entire factions at the cost of great consequences. But no, instead they'll just respawn minutes after you spent hours clearing out their base.
Be aware of these faults, but don't let that dissuade you from playing Clear Sky. It is an incredible experience that needs to be experienced. If you want a deep and immersive game, this is most certainly it. The game needs to be played. The thing is, it also needs to be modded.