After I mentioned Unigine Heaven & Valley now running on Radeon Gallium3D quite well for the imminent release of Mesa 10.1, Phoronix readers were quick to point out that as of a few days ago Metro: Last Light is rendering correctly with Mesa drivers.
Following some changes last week, the current Mesa Git code should be in good shape for this exciting game. The latest fix will not be limited to Mesa 10.2-devel but is material for backporting to the current Mesa stable release series. The change ended up being Mesa relaxing how it handles dual underscored macro names in GLSL with confusion over the GL Shading Language specification and the binary drivers treating "__" macros fine where as Mesa was previously generating an error if it wasn't a keyword.
Activity surrounding Metro: Last Light on Mesa/Gallium3D drivers can be tracked via this bug report and it appears for the RadeonSI, R600, and Intel drivers the game can now run, albeit performance might be another story. Unfortunately there won't be any Metro: Last Light Linux benchmarks in the near future on Phoronix... First of all, there's the Steam benchmarking challenges plus the Windows utility that shipped as part of Metro: Last Light isn't part of the ported Linux game. See Running Benchmarks On Other New Linux Games for more details.