Does a game "run on Linux" when it has 100% feature parity? 90%? 80%? What are you willing to cut? Some performance? A few graphical effects? Multiplayer?

When you look at the details, Linux gaming is not as good as it might seem.

But I'm still gaming on Linux!

What you sacrifice in feature parity, you gain in user freedom and principle. To me, that is a worthwhile tradeoff. Especially since it's really not that much different at this point. You're not sacrificing much in most cases now. It's really quite remarkable.