Just checked - officially just under a third of my library has *nix compatibility. Impressive compared to my 10% estimate, broken compared to the 100% windows working.
I'm hoping things have changed, but based on my last linux gaming adventure I'm very wary - seemed like a complete crapshoot as to whether your distro's audio and gfx setup aligns with the game and even then the FPS rate is a complete luck of the draw. And god help you if you're not on a standard ubuntu gnome setup...