We knew it was coming and today it finally is publicly available... Metro: Last Light is available for Linux gamers via Valve's Steam client.
Metro: Last Light is a first person shooter / horror video game developed by 4A Games that premiered for Windows and Xbox 360 / PlayStation 3 earlier in the year. The post-apocalyptic video game powered by the 4A Engine has been ported to Linux over the past few months
More details on Metro: Last Light can be found via the SteamPowered web-site
or the game's website