Since July there's been a Witcher 2 beta offering up many improvements to better the performance and playability of the game on most Linux hardware. The last beta update to talk about was in mid-August when the game's performance continued to rise. Another beta update made it out today and again the focus is on increased performance.
Today's Witcher 2 Beta 5 (Build 370876) works around an AMD Catalyst Linux driver bug that has broken ARB_texture_storage support. The game is now detecting the Catalyst driver and disabling usage of this extension, although AMD told the developers that the GL extension will be fixed in the next Catalyst driver release. As explained via the OpenGL.org registry, "This extension provides a mechanism for specifying the entire structure of a texture in a single call, allowing certain consistency checks and memory allocations to be done up front. Once specified, the format and dimensions of the image array become immutable, to simplify completeness checks in the implementation."
The second change to this new beta is changing the game's memory management handling, which its developers found now to be faster. More details via the GitHub announcement.
You can find The Witcher 2 on Steam for Linux for $20.