It seems like every time I try to uninstall a game but choose to keep my saved games, it comes back with "uninstall failed" and a retry button that never works. Then if I go into the actual folder and use the uninstaller there, it says it uninstalled it and I can see there are fewer files... but the folder still takes up just as much space as before. Somehow I doubt just the data for my save game is taking up multiple gigabytes. The only way to ACTUALLY uninstall anything is to straight-up drag the entire folder into the trash, and lose my saved games with them. What's wrong with Galaxy that it keeps doing this?

Check your HDD/SSD physical health with CrystalDiskInfo and your file system health with chkdsk.

It's not a hard drive issue. If I drag the folder in the trash and delete it, that space is immediately freed up. The problem is that the uninstaller appears to delete some files that don't take up enough space to know about, while leaving the vast majority of the game intact, yet still tells me it uninstalled the game (unless I try to uninstall it using Galaxy, in which case it just fails for no reason). I use other clients such as Steam on the same hard drive and there's never any issue like this.

Edit: I did as you suggested too, since hey, seems like a good idea regardless. Everything checked out fine.

Good.

The only suggestion you may not have tried in the Uninstall failed E15 support article is to restart GOG Galaxy after manually running the uninstaller in the game's folder.

If you haven't already, open a support ticket. Zip up and attach the C:\ProgramData\GOG.com\Galaxy\logs folder to your ticket.