what I notice so far is the missing language files besides of english. 800 MB less than previous version for me. But after update today the game does not start anymore. Even when executing the .exes in the main dir and the bin dir. The GOG "Play" button just goes violet again. Anyone else experiencing this?

What's the version you are having this problem with?

the version is 1.6.0.2

now I completely uninstalled the game (6.300 MB), did a clean install (also 1.6.0.2, ~ 6.020 MB), but have to run the Stalker-COP.exe as admin to get it working. I was wondering about the Settings.exe, that seems to allow a language change, but has an empty entry field for a serial number.

Glad, that it works now.