As a gamer, I try to incorporate Linux as a gaming OS. Taking baby steps.
Firstly, the UI's. I hate Unity. It's ugly and not something I can use comfortably. XFCE works really nicely, but looks like Windows 95 by default. MATE is pretty nice overall, but has some strange bugs and looks 5 years dated. KDE is nice looking, but has some strange issues as well. Cinnamon by MINT is very nice looking, but works horribly with graphic cards. So far my best experience is using MATE or XFCE, but with Mint. They can turn an ugly UI into something I can look at.
Secondly, Windows compatibility. I am not going to hold my breath over new games being ported over to Linux. WINE needs to work better and easier. It should be as easy as installing Wine and running the Windows applications. Otherwise I might as well go back to using Windows.
Finally drivers. I love the open source drivers for AMD, but they can be a problem. They don't always work, and they lack control. There's no UI to allow me to adjust things like AA or other features. The oibaf drivers can sometimes break things. I also have a laptop with Nvidia 9600M GT, that it took me a while to figure that the 304.121 drivers are the only drivers that work with 3.14 kernel.
If Steam wants to break past 1% with Linux, these 3 things must be addressed.