They're definitely not pushing the engine to its limits and it's a shame. No Ray Reconstruction for example and no hardware ray tracing. I was wondering why shadows and reflections lacked clarity at first. This is apparently why.
It's a weird one though because despite all the flaws I can't stop playing the game. Maybe I just love STALKER that much. I also have a bunch of mods installed, granted.
No, but I would have if I had fewer hours played just to get a proper experience from the start and consequently less of an item stockpile etc. Grok's less loot in stashes won't apply retroactively for example.