Ok, first of all: This is a STALKER game, so it's good - basically. But there're issues that need to be adressed: Even with the latest patch and with fan-made mods, there are still a lot of bugs. AFAIK most if not all of them are hardcoded, so I don't think they'll be resolved. The faction war system is broken beyond repair in my view. As a consequence some side quests aren't available simply because the NPCs won't do what they're supposed to. Faction missions spawn all the time with no time to react to them. Sometimes quest rewards don't appear. Scopes don't work properly. Sometimes nearby neutral NPCs turn hostile for no reason. And so on...
That said, if you're a fan of the series and have a certain tolerance for bugs, you might very well enjoy Clear Sky. Especially for SoC veterans the storyline is quite interesting to say the least.
If not, well, you can simply skip this 'black sheep' and play Call of Pripyat. Since CS is a prequel to SoC and CoP takes place afterwards, you won't miss anything important.