Lately I've been playing a lot of Team Fortress 2. Until quite recently, I've been having to make a tough choice. Use Windows so I can play those games, or use Linux and not be able to play it. Valve has had Steam for Linux in public beta for a while now, but I haven't used it since I was first added to the beta until today. While I can't make a comparison between then and now, because I upgraded my graphics card, I can say that Valve is doing extremely well in porting TF2 over to Linux. I feel that this is an important step in making Linux a more viable option for many mainstream computer users/light gamers. While the performance of TF2 on Linux is not quite on-par with that of TF2 on Windows, it's still very playable and enjoyable.
If anybody is wondering, I upgraded my graphics card from the integrated 2500 HD graphics on my i5 to a GTX 650 - It's certainly nothing high-end, but it gets the job done. I had to install the beta drivers from Ubuntu's proprietary driver window, because the stable version didn't work.