Metro: Last Light is the sequel to the 2010 game Metro 2033, which was based on a post-apocalyptic science fiction novel of the same name.
Together with the trailer above, THQ is offering free Steam copies of Metro 2033. If you want to grab a copy of the first game, all you got to do is head over to Metro's Facebook page and like it. After doing so, you will be given a Steam redeem code.
I highly recommend you try Metro 2033 if you haven't yet. It's a great shooter with an eerie atmosphere and that need to save up on ammo to survive.
Metro: Last Light is planned for a March 2013 release on Playstation 3, Xbox 360, and PC.