I'm in the middle of Chapter 2 on Difficult setting so far, and I'm having a good time! Really amazed by how much the Goldsrc engine can be pushed decades later.
Anyone who wants to play on the Steam Deck or Steam Machine, you simply need to launch Diffusion-x86_64.AppImage through Steam shortcut while in Gaming Mode. You can also launch through Konsole in the game's directory folder with right-click menu, or with the command "exec ./Diffusion-x86_64.AppImage".
A small suggestion for the mod option screen: have a toggle for hud_fastswitch, for players who want to use a controller. It's easy enough to change if one knows HL1 console command, but that's not everybody.
Otherwise, great mod! I'm getting slight FEAR 1 vibes in terms of combat (without slow-mo) and level design.