I'm trying to download the game for the first time. While installing, GOG crashed.

Now, I have "Play" button greyed and non-clickable, near is the "Installation error" message.
Tried to check/repair - it checked for the local files and said the same "Installation error". Also tried uninstalling inside GOG - same result.

Though, I can run the game via opening it's folder and opening the .exe file for it.

Any suggestions?

I recommend submitting a support ticket. In the meantime, you could always just make a shortcut to the .exe file and run it from there, unless you care about the achievements.

I do, I guess. Also, I'm playing on 2 PCs, so Cloud saves would be a great feature.

Thank you for the recommendation, already done.