It didn't happen overnight, but Steam's catalogue of Linux games has grown significantly over the last few years, no doubt helped by the release Value's Debian-powered SteamOS. Abandoning Windows for the open source platform was once the quickest way to gaming frustration, be it a lack of native ports or wrestling with the likes of Wine or other virtualisation option, but with almost 700 working titles available, the variety is certainly there.
If you hit up SteamDB's Linux page, you'll find a robust list of games for the operating system, with 863 at last count. Of those, 676 are "confirmed to be working", but that's still a healthy number.
It's not just indies or esoteric games either, with Borderlands: The Pre-Sequel, Serious Sam 3: BFE, Company of Heroes 2, Baldur's Gate II: Enhanced Edition and plenty of others representing the larger developers and publishers.
The question is though: Could you dump Windows today without sacrificing your ability to game? Sadly, the answer to that is no. Don't get me wrong, you can definitely live it up on Linux, but if you just want to download a game and play it, your experience is going to be smoother on Windows.
The gap is narrowing, though.