Valve released what is probably the biggest development in PC gaming this entire decade, the official release of its Steam content distribution platform, for Linux, particularly targeting Ubuntu, a popular personal desktop Linux distro. The client ships with a formidable contingent (over 100 titles) of games, including a few of Valve's homebrew ones from the Left 4 Dead franchise.
A killer feature here is SteamPlay, which rids you of the need to purchase Linux versions of the games if you already own the Windows or Mac OS X versions. If you happen to frequent any of the 101 games on offer, on Windows, and want to switch over to Ubuntu, Steam for Linux gives you a solid reason to.
Development of Steam for Linux, and porting of Windows (predominantly Direct3D) titles over to Linux (which has OpenGL as the most feature-rich graphics API), was accelerated when NVIDIA chipped in with some developer help. Refined GeForce drivers launched by the company beginning late-2012 boosted game frame-rates by over 100 percent, and so Valve, as a token of gratitude recommended GeForce GPUs and NVIDIA drivers for best/stable performance.
Steam for Linux can be downloaded from Ubuntu's marketplace, and from here.