stereophil: I got this "Essential components needed to start GOG Galaxy are missing. Please reinstall the application." error. So I did what the message suggested and reinstalled GOG Galaxy into the same initial installation folder which was called "Games" and contained ALL the games on my HDD. After installation I saw that Galaxy apparently deleted everything else in that folder. Now I have a "Games" folder with just the Galaxy client in it. All my GOG games, all my Steam games - gone.
I've always been an ardent supporter of GOG, but now I have to say that I'm a bit pissed off. :(
EDIT:
To clarify things, this is what my setup looked like:
D:\games\GalaxyClient
D:\games\GOGGames
D:\games\Steam
D:\games\[some other game-related stuff]
Actual games from GOG were installed in \GOGGames. Now, after reinstalling (where I didn't change my install directory D:\games\GalaxyClient - I thought "why should I?") it looked like this:
D:\games\GalaxyClient
Everything else in D:\games\ was gone.
Not so much for the games, but for anything else you have from your games folder that you may find difficult to get back use Recuva.
It will simply scan the drive for deleted items. So long as Galaxy just did a normal uninstall on the folder you should be able to get stuff back.
Please do read their instructions on recovering you data, such as you will need a separate drive to recover the data too. Even an SDcard will do.