http://store.steampowered.com/app/286690/?snr=1_4_4__131

It also looks like there's a $7.50 package that includes Last Light as well. It's until the 16th.

It's apparently one of those dystopian FPS-RPG shooter types:

In 2013 the world was devastated by an apocalyptic event, annihilating almost all mankind and turning the Earth's surface into a poisonous wasteland. A handful of survivors took refuge in the depths of the Moscow underground, and human civilization entered a new Dark Age.

The year is 2033. An entire generation has been born and raised underground, and their besieged Metro Station-Cities struggle for survival, with each other, and the mutant horrors that await outside. You are Artyom, born in the last days before the fire, but raised underground. Having never ventured beyond the city limits, one fateful event sparks a desperate mission to the heart of the Metro system, to warn the remnants of mankind of a terrible impending threat.

Your journey takes you from the forgotten catacombs beneath the subway to the desolate wastelands above, where your actions will determine the fate of mankind. But what if the real threat comes from within?

I've heard nothing but good about the game itself, and the redux is supposedly is a nice update. I'm looking into buying it myself (even if I gotta save for new gaming headphones).