Uninformed individual talking.
Is the Steam Controller compatible with GOG games on the current version of Galaxy (I have 1.2.59)? I ask because I got a Steam controller during the recent sale and I want to know if GOG games treat it similarly to how it treats an XBone or 360 controller.

Thank you ahead of time.

my guess is youd get better results if you ran the gog game as a "non steam game" through the steam client due to steam having additional client based support for controllers as a whole.

out of the box id guess compatability will be hit and miss.

I'll be trying it out once mine arrives (they warned me it'll be a while). 5€ instead of 50? Yes, please. Even adding the 20€-or-so shipping, that's a good deal compared to most other gamepads.

My Steam Link has mostly been collecting dust, waiting for this.

Isn't the Steam controller dependent on the Steam client for anything more than basic functionality? I mean, I assume it has some kind of basic xinput mode, but maybe not?

It definitely works. You'll have to use the Steam client to the best out of it but it's worth it. So many options.

I would also suggest picking up Controller Companion from steam if you don't already own it. It only costs a couple of dollars, and I have been using it for a long time now and love it. Not only will it work with any game you play, whether it's steam, GOG, or physical disk, but you can use it to map a controller to play old games with no controller support with one. You can also just use it to control your pc with a controller which is convenient sometimes as well.

There are third party tools available for configuring the Steam controller, such as this one: https://github.com/kozec/sc-controller