Ok so I go to install a game I downloaded. Go to install it since my C drive is an SSD drive without much room I am installing on a 2TB Hard drive Drive G. Oh the installer runs out of room for the temp directory? Steam does not use the Temp directory for installing so why is the stupid GOG requiring Temp directory for installing? This means I can't install as the free space on drive C is too small for the game to install when I am installing to G: drive.

I have never had this problem with anyone else's installers just GOG.

There are two ways to solve this problem.

Move the location of your %tmp% and %temp% directory from C: to any drive you got plenty of space.

Win-key + R .. sysdm.cpl ... Enter
Environment Variables... ... for both TEMP and TMP ... Edit - D:\foldername

Get yourself acquainted with Innoextract

Have you tried setting the TEMP and TMP variables?

Hell, have you tried searching?
I just now tried duckduckgo.com, and the two top hits were: in these forums and on Reddit.

And to answer your question: Of course their installers are crap. Most of the stuff they say, do or make themselves seems to be somewhat below average.
Come for the DRM free games, stay for ... DRM free games.
Not much else to recommend GOG for. But DRM free is a big enough deal for some of us that we'll put up with lots of issues we wouldn't otherwise accept.

Edit: OK, Mori_Yuki already answered. That'll teach me to answer a post in an old browser tab without refreshing first. :)

I've recently purchased and installed Control with the offline installer on D:, I didn't have this kind of issue (even though I had 350GB free on my primary SSD disc)

It's not really a GOG installer, it's an Inno installer.

Question @Molitar:
Where is your Download folder, on which drive?

i mean the problem occurs only if a file within the Offline Installer archive does'nt fit on the drive where your temp folder is. i had this for example with Ghostrunner which contains one single file with about 20 GB in size.

to be inline with everything else?:P

I love their installer. With appropriate software I'm able to extract files without need of installation. Something like portable game:) Not working with every game but most of mine are OK.

Clearly you do not have as much free space on your System drive as you should have ... not a good idea, regardless of GOG's InnoSetup installers.

You will find your PC will run much better without the System drive being too full ... a well known Windows issue.

You should try old DotEmu installers some time.

I don't remember which game it was, but the installer had five languages in it, and it unpacked all five in temp folders, but actually installed only one of them. Those temporary files took much more space than the actual installed game did.

GOG's installers have their own issues, but it could be worse.

Pretty much every installer will copy itself to your Temp folder and then run the .tmp file created. It's most likely that you've only noticed the problem with GOG installers since they can be so much larger than most others.

As well as modifying your TEMP/TMP variable as suggested above, you can also use a tool like Link Shell Extension to replace your Temp folder with an NTFS junction to another disk on your system.
Heh - reminds me of Supreme Commander which installed help videos and voiceovers for 5 languages. I was able to save over 2GB by removing the ones I didn't need.

Steam doesn't offer any offline installers for its games, so you can't compare how it does things.

As already pointed out, either move your TEMP-directory in Windows to some other drive where you have plenty of room, or use Galaxy to install the game. Using Galaxy has a similar idea as using Steam, ie. the client "streams" the download directly to the target installation directory.

Yes I guess GOG could probably design the offline installers differently, so that they would uncompress the files directly to the target directory and then run some script that puts all necessary registry entries etc. in its place. Not sure if doing it this way has some downsides too.

One exception though (which is why I presume GOG first uncompresses everything to TEMP directory before actual installation): if the game installation includes installers for dependencies like DirectX, PhysX, MS Visual C++ blaa blaa etc., I guess their installers would need to be uncompressed to the temp directory anyway, before they can be run.

To help you clean up space on your C: (where your temp directory is located), you may want to run Disk Clean-up in elevated mode. You could also remove some of the Windows system restore points.

As other posters have already said, try to keep a bit more spare space on your C: - it's not good practice to run close to full.

Disabling hibernation and removing hiberfil.sys can free up more than a hundred GB worth of precious space! Something many don't even know about because it is a hidden file.

Right-click on the Windows icon ... Windows Power-Shell (Administrator) ... enter powercfg -h off ... dir \ enter ... dir -h enter ... del hiberfil.sys if it hasn't already been deleted. Consider restarting your system after this change has been made.