Such as Tower of Time and Turok 2 (on my machine at least). If I add them to steam, then they don't work (even though hundreds of others do) Does anybody know why?

What issue are you having ? They don't start at all or something else ?

Don't we all love when spambots pretend to help diagnose computer stuff?

Anyway, have you tried running them directly from the EXE instead of through Galaxy or Steam? Note that if it works you won't be able to use Galaxy's features like achievements or cloud saves, but at least it will help us diagnose things better.

If I recall correctly, when you install games through Galaxy, the launch parameters of the games include starting up Galaxy first along with launching the game.

I recommend you install the games through the offline installers instead and uninstall Galaxy.

There's a thread about DRM in single player games already.

And while it's true that there are a few games that only offer certain content when a connection (Galaxy for example) is active and a few less that are completely fucked up and would for example not save options (Saints Row 3 remaster) without Galaxy, it is a rule of GOG, that games must be playable offline.

Turok 2 I played without Galaxy and it works just fine.

No idea why Steam can't run them. Ask Valve. For the link on the desktop that is true.
The link in the game directory however ("Launch XYZ" does not include a Galaxy call).

It's a good suggestion in any case.

I have tried that but to no avail. I've just found another game that only launches through Galaxy on my machine: Yooka Layle.

This one works fine without Galaxy for me.

But there are probably two main differences between your system and mine:
- I never installed GOG Galaxy
- I do not use Windows

same

@psadler Try to double click on the .exe in the games directory.

I don't have Turok but Tower of Time and Yooka-Laylee work fine without Galaxy here.

Do you have a firewall installed that restricts access to localhost? That can be a problem for some games that still have an older Galaxy library linked to it. See here.

Short version: Make sure your firewall allows access to localhost for these games.