Steam now offers a Linux and SteamOS version of The Witcher 2: Assassins of Kings Enhanced Edition, CD Projekt RED's RPG, which is currently on sale for 80% off (thanks Xil). This currently only supports NVIDIA cards, as is explained by this developer post from jaycee1980:

The current AMD Catalyst driver contains a problem which stops the game from running. AMD have already fixed the problem, and the fix will be in the next driver release.

Intel is not supported simply because the driver performance is currently insufficient to run the game well enough. It will run, but the framerate is not good.

The open source Nouveau and Radeon drivers are simply not feature complete enough to run the game. Witcher 2's RED Engine is making full use of OpenGL 3.2 features.