So, yeah that's basically it. The game starts in windowed mode and it's fully playable in its default 1280x720 mode, but whenever I try to change between resolutions or going fullscreen, it closes itself.

I found this - https://steamcommunity.com/app/253150/discussions/0/624075036387490743/

Windows: We experience some problems with fullscreen modes on high-dpi systems running Windows 8.1 when using desktop scaling of 125% or larger. As a known workaround you can:

Right-click on Halfway in the Steam library, select "Properties", then navigate to "Local Files" / "Browse Local Files"
In Windows Explorer, right-click on Halfway.exe, select "Properties".
In the "Compatibility" tab, check "Disable Display Scaling On High DPI Settings".

Just ignore steam part and find Halfway.exe, right-click on it and continue as above. ;)

Thanks for your help, but what I had to do is edit the settings.json file to make the game run in fullscreen from the start, and from then on I could change to whatever resolution I desired :D

2021 and still, and it has mouse acceleration as well. This is basically unplayable unless you're used to playing 90's games with terrible software cursors and input lag.