I think it was world of warcraft. As a kid I had a very bad computer, so windows (Vista I think ?) Gave me something like 15 fps while Linux+Wine gave me 20. It already felt like wizardry that I had better performance while needing a compatibility layer.
I have also some memories of discovering a new land of freedom. When i plugged a CD from the library, Ubuntu’s default music player had a popup “wanna install anti-DRM plugins & make a copy of those tracks?”