I was amazed yesterday. I tried L4D(1) on native GNU/Linux Steam (Ubuntu) and it just worked after installing the game, zero tweaking. No need to set up Steam for Windows with WINE or anything.
I plan on trying SteamOS (since I only game, sit on discord and browse internet), just don't feel like installing it to find out nvidia drivers are not supported, so I'll just stick to Windows for now
As a complete casual Linux user (made the switch last year), all the games I previously played on Windows work on Linux smoothly with minimal or no intervention on my part. Even started fiddling with emulators - Legend of Zelda BotW on yuzu worked right out of the box