Recently I found myself using Linux more and more often. While being a gamer at heart, and since most PC games are made for Windows, I wanted to give a go and see what could I do while using Linux. True that more and more developers, specially Indie developers, are making versions of their games to Linux, it still is a very short list while compared with Windows. For example, in Steam at the moment there are about 100 games (with Downloadable content in the counting) and most of them are little know titles for most audience, like World of Goo or Cave Story +. There are a few exceptions however, being the most notorious, Crusader Kings 2, Team Fortress 2 or X3: Albion Prelude. And even those, except for Team Fortress 2, most are regarded as not AAA titles.
However, and I guess due to Steam support over Linux games, and also because there has been a sudden increase on Indie games being produced, I believe the number of games on that platform for Linux will increase exponentially over the time.
Another platform, also boosts a considerable list of Linux games, Desura. This platforms hosts a big list of Indie games, and part of these titles also run on Linux. And there is a fair amount of users that request developers a port of their game to this system.
On the other hand, there are alternatives. WINE (an acronym for "Wine is not an Emulator") is, has said in the website, "compatibility layer capable of running Windows applications on several POSIX-compliant operating systems, such as Linux, Mac OSX, & BSD. Instead of simulating internal Windows logic like a virtual machine or emulator, Wine translates Windows API calls into POSIX calls on-the-fly, eliminating the performance and memory penalties of other methods and allowing you to cleanly integrate Windows applications into your desktop."
So, given that jargon, we can say that WINE allows Linux to run Windows games. It's not that easy though. You will have to run some configuration over WINE to allow the game to perform under Linux, and for the most of it, for a newbie Linux user like me, it's a bit complicated. There are several sites that go over this, and enough to read and learn about, so I guess if you are persistent, eventually it will pay off. For me, all I tried, I still managed to get one title running, and it was Guild Wars 1. But to be fair it didn't required any tweaking, it just run fine. I also tried Eve Online, but whenever I was about to actually log in the character, the game would just close.
A personal hope, is that in a near future, Good Old Games, would start supporting Linux. I dunno if that is possible, but they did recently start supporting Mac, so my hopes are high on this happening.
Overall, I think gaming in Linux is still it's early infancy, however I think it's been on infancy for far too long, and it should start to grow a bit now. For a system and from my own knowledge I think Linux is far more stable and fast then Windows, but a bit obscure on the way it works. But since I'm a newbie in Linux I'm holding it.