Two of the most iconic and beloved FPS games ever made, together at last. Half-Life: Crowbar - Deep in the Dead is a Half-Life mod that transforms Valve's classic from a hellish survival game on Earth to, well, a hellish survival game on Mars.

The mod converts id Software's Union Aerospace Corporation's waste facilities into the cleaner, greyer corridors, offices, and parking lots of the Black Mesa Research Facility. In the demo, you play-through a melding of Half-Life's opening chapter with Doom's E1M1, wherein some scientists open an inter-dimensional portal for horrific creatures to break through and, when you really get down to it, there's not a huge amount of difference in context between the two old games, is there?

A cool thing about Half-Life: Crowbar is that you aren't Gordon Freeman, or Doomguy, you're engineer Dr. Stan Blazkowicz, an homage to Wolfenstein protagonist BJ Blazkowicz, who adorns the Doom suit where Freeman got his HEV outfit. You're not the one who pulls the lever like in Half-Life either, rather just someone stuck in the middle of a very unfortunate situation, having to crowbar and shoot your way through a large number of headcrabs.