If you hadn't already named your own price for Metro 2033 in the Humble THQ Bundle, you now have a chance to pick up the post-apocalyptic shooter completely free.
An advertisement on the game's facebook page, also accessible by via the URL freemetrogame.com, is offering players a Steam download key for the game, simply for clicking "like" to follow their social updates. According to the small-print, the offer ends on December 16.
The promotion serves to prime players with the game's chilling narrative in preparation for the upcoming sequel Metro: Last Light, which is due in March 2013, for PC, Xbox 360, and PlayStation 3.
The latest trailer for Metro: Last Light, titled Genesis, can be seen below: