Oddly I found the story interesting, but harder to follow in COP than the others. Some complex parts when looking at how all the games tie together but in general pretty simple yet, to me, still somewhat engaging. However, you did call it, the enviroment is what has elevated the STALKER games to some of my all time favorites, even clear sky. You can ask my wife, as soon as COP was announced she asked about the release date in the US so she knew when not to schedule anything for us
At this point I've played through SOC twice (both times with complete), CS twice (first time vanilla, second time using complete) and COP once vanilla. LOVE the games.