While I agree that there are more and a more games coming to Linux, even big AAA game check out Borderlands, XCOM, Valve, and a few others standing out from the crowd, I still feel that until Linux supporters and developers sort out a "universal" way to make it happen and be up to date it will still be just a hobbyist thing rather than a real competitor in desktop/PC gaming.
I say this not as a complete noob on this side of things, but as an outside observer with out the dev knowledge, what I see is not promising. I know I will be told by people who are into this I am wrong but this is just how it looks.
There is not a reliable, in the sense that it will be up to date and supported, graphics API. I know I can hear it all ready. Yes there is Open GL, it is frankly out of date. And yes Vulkan will save the day I know, but where is it? I know they are working on it and it is supposed to be good, but there is no real world, by which I mean not just a tech demo, games with it that I can play and compare to the same game running DX 11, 10 or 12. Or even on different OS's At least not that I can find.
And the drivers (while in varying quality on both vendors) are not up to scratch, not aweful but not quite good enough to keep an avid gamer, who can get high fps and quality on another OS, on Linux because it is better else where. I say this not as my own opinion, I very much like Linux and where it is going, but as a view in from the outside with no knowledge of the current goings on inside the free and open source world.
Although I hear kernel drivers are coming soon for AMD at least that are supposed to be a big step up, I look forward to this and hope it is part/sign of bigger things and more support coning from bigger developers.
Yeah this could change in the space of a year but I just don't expect it to happen at a high enough rate and level of quality that will draw over the gamers that like their graphics and could care less about ethics, open source, speed, compatibility, and all the other fantastic benefits of linux. For them the best option for range of games with the most and highest quality settings for visual effect is windows. Linux just is not fast enough and pretty enough for them. I hope this changes but what linux desperately needs right now is feature parity and speed parity or excess. When both option looks the same, have the same visual options and run as fast or faster, then gamers will move over from windows.
Just some thoughts and opinions.