I have this registry key problem everytime I try to install FEAR 1. Any help will be appreciated...

P.S.: there's also a game launcher that I use called Playnite that has trouble seeing it as being installed (before this issue occurred).

You could try to install as administrator.
Though this is really more of a question you should contact GOG's technical support with :-)

Did that, even through backup copy and removed the period sign from the title, it still gives the same registry key problem but this time for the uninstaller <.<"

P.S.: I actually did send 'em a support ticket.

The off-line installer worked for me.

After it's installed, make sure you install the unofficial slow down fix.

It's working now (through galaxy), strange. I'm pretty sure I have the client excluded from av/firewall; must have been a corrupted registry when I tried verifying the game's integrity...