So I tried installing ReShade on Half-Life (Steam) and it kinda works.
Kinda
It's basically running twice, one copy over the other.
Samples
I'm putting some logs and more sample images for now. I'll look into it more on later.
More samples + logs
Funny thing is the game is OpenGL but still loads dxgi.dll for some reason. Also ReShade gets confused because of this (check the extra samples to see what I mean)
PS: On one of the logs you'll see error about missing texture "DirtA.png". It doesn't change anything.