For those like me who were never sure if they would like (or could run) Metro 2033, we can find out with this hefty 2.94GB demo. From the game description:

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 your Metro Station-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.

You can download it now locally from AusGamers (with a few other mirrors available there too). promoted/edited forum item