Metro: Last Light is powered by the 4A Engine, having been developed by the 4A Game Studio. The game was originally released earlier in 2013 for Windows and game consoles but has now been brought to Linux via Steam. Firing up the Steam Linux client today will reveal this new Linux game title.
Update: At this time the SteamDB listing for Metro Last Light on Linux is in place but it doesn't appear the Linux game binaries are yet uploaded.
what the.. unexpected of what?!