It seems that a portal transfer went wrong or at least not as exactly planned and you find yourself in an underground base. Find your way around and see what you can discover.
From the title I was rather hoping for a romp on the red planet, with views of burnt orange skies and red-brown sand. Or at least a small glimpse. Surely not too much to ask? I was sorely disappointed on that front in a big way, with the entirety of the mod set in one large-yet-strangely-claustrophobic underground base (how cliche) overrun with zombies. Zombies on Mars! Yeah, because that formula aaaaalways works. Like, for example, The Last Days On Mars?
Alright, rant over. Now to get to the actual evaluation.
Overlooking the expectation-raising title, the mod actually stands up pretty well as a standalone. G is used very effectively but I think the zombies are a little overused in the mod, and the last 5 minutes of the game don't make that much sense, though I will say that they are epic as f**k. That last battle with the Combine, the way the alarm starts when the beat drops and the doors open and they just come swarming out at you, that was just incredible.
On the whole, it's very well executed and includes some intriguing new features that you don't often get in your bog-standard Source mod, but the title seemed to promise better things that the final product just didn't deliver. If it had been titled something along the lines of "Yet Another Underground Suspense Map" I wouldn't have been so annoyed. But if you put Mars in the title, we want to see red dammit! Where's our big red rock?