If any of those games have sourceports, you can just extract the files you need with inno-extract and avoid seeing any ads altogether!

https://constexpr.org/innoextract/

Innoextract extracts files from Inno Setup installers, which is what GOG uses for the games it sells.

I think you are being a little picky (no offense), is just a way to advertise their product in exchange for an offline installer, other stores (Humble Bundle or Itchio) just give you a .zip or .rar file, you can always use GOG Galaxy 2.0 or just put some music, see some videos and forget about the installer.

But I like seeing the Duke Nukem Atomic Edition ad pop up in offline installs. Even though it hasn't been in the store for six years and might be considered false advertising

Do you really live in the Pitcairn Islands?

Aside from the fact that there are games advertised in the installers which are no longer sold here, there's the issue of installers having a wildly variable number of games in the carousel -- some feature more than a dozen, while others cycle through the same three or four titles at least half a dozen times during the installation process. And let's not get into the fact that clicking the "Download now" button (which really should be "Buy now" or something less misleading) apparently tries to open the GOG store page in Internet Explorer specifically, even if your default browser is set to something else (which, hopefully, it is!). (I don't know what happens on Win 10, or any other Windows install from which IE has been excised, or programs blocked from accessing it somehow.)

But apart from those "things which should not be", I don't really see the problem. As long as there isn't blaring audio during the installation process, and the ads neither increase the size of the installer files(s) much, nor create a heavier load on system resources while running, I don't much care.

What I wish GOG had was the original DOS installers as *.IMG files so i could use D-Fend RELOADED and Munt or my custom Ultrasound files in the ultrasound directory

from Arachnosoft to use with Munt
arachnosoft soundfont

I see. I guess that's what you'd have to create and adapt to the individual project. Software allowing - in a best-case scenario - you would be able to write a generic template, applicable across all projects. I bet many would love to see something like this being released. OP sure would. ;-)

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Here is a solution for OP. Open a command prompt window, Win + R, cmd, Enter. Change to the path to your setup file, Enter setup, press Tab-key to auto-complete it, so it looks like this on your screen: "setup_game_name_1.0_(43163).exe".
Enter "setup_game_name_1.0_(43163).exe" /VERYSILENT and enter. The setup should start, allowing you to select the language, press O.K. as usual and setup will start. You will see no installer window and get no messages like "Installation has finished ... Close | Run. When you see the icon appear on your desktop will you know that installation was successful. Or you could open taskmanager and see when the setup.exe vanishes to know that installation was finished.

There might be other command-line switches that do what you want, have the installer window open, but without showing any ads. See attachement for the others.

I dont even watch em , just start installer and alt tab back to browser or vid player

Probably make a batch file which will do that for games, though you'd likely have to drag and drop...

Alright tested it and it seems to work. At least in my initial tests (included) and further not included.

So... Make a batch file as 'GogNoAds.bat' with: Lastly drag and drop exe installer onto the icon/batch file and Poof!

edit: Though tried to install with Dust, and... Hmmm.. Other than confirmation to run it, nothing happened.... Maybe this isn't the best solution...

As long as they aren't overly erratic and only cover games sold on GOG, I don't mind. Like others that mentioned a certain nostalgia for it, it's nice.

Well preferably games that are related. Say if you got Baulder's gate, then suggesting other D&D related paraphernalia, or RPG based. If you did sidescroll action games, other similar ones. Tactics? Suggest other isometric and tactic games, etc.

What would be the point of only showing you games you're already likely to own? Even if you don't own them, they want to show you other things you might not normally play and find out what catches your eye.

Even a grumpy old bastard like me don't mind the ads when installing GOG games. I mean, at least the ads are potentially relevant to my interests.

This method isn't ideal but works. Problem being that there is no window with progress bar. There is the additional /LOG=" " so with "%~1" /VERYSILENT /LOG="setup.txt" you at least get visual feedback.

For OP the ideal solution would probably be an installer looking and behaving like the uninstaller: No ads, progress bar, prompts. That, of course, isn't going to happen. ;-)