Download SRP with or without some of the included optional files for the best vanilla experience

best game in the series no doubt

Clear Sky is primarily an action game, and its design reflects that. The introduction of features such as fast travel let you skip Shadow of Chernobyl's walking simulation, and point you towards the action gameplay. Weapon/armor repairs and upgrades give you a reason to seek out modes of income; the faction wars provide such, and they additionally net you exclusive rewards. Secondarily, Clear Sky packs in a bit more exposition; you encounter Freedom and the Mercenaries within the main story, for one. The former were completely possible to ignore in SHoC (and perhaps ideally so, as the game's midpoint is the Duty base) and the latter only present for a brief skirmish.

Fundamentally, CS is solid. It falters in the execution of its new mechanics; the faction war can largely be ignored (I did, anyway), and suffers from redundancy thanks to a never-ending cycle of base capture and defense. The threat of emissions seems to hamper your momentum. Artifacts now want to drench you in rads. Perhaps its greatest fault is the plot; not to say SHoC was spectacularly written, but the pacing suffers near the endgame where the action is turned up to 11 and the game seemingly ends (or not at all, since it is possible to softlock yourself within the finale) on a whim. CS is still a STALKER game, however, and thus worth playing. Install SRP.