This week as promised Valve has released Alien Swarm for free, and it is pretty much the best thing to hit Steam since Left 4 Dead 2.

There. I said it.

Despite the fact that it is incredibly short out of the box, (just a single campaign that took around two and half hours on Hard) it is an incredibly fun four player co-op zombie survival alien blasting experience played from a top down perspective. It also happens to be incredibly pretty to look at (it’s built on the latest version of Source, even newer than Left 4 Dead 2′s version) and comes with the easiest map creator in the world. Expect to see literally hundreds of custom maps, campaigns and mods in the coming weeks following its release. I personally can’t wait to see Left 4 Dead campaigns work their way into this title – zombies and all. That would be so much fun I don’t even know where to begin. Not bad for a free title, eh?

So we have a completely free, professional quality downloadable title (that is shockingly similar to the $15 downloadable Alien Breed: Impact), which also comes with the entire source code and the latest version of Valve’s Source Development Kit.

Everybody with a PC should must download this on Steam (it is completely free), and experience Valve once again raising the bar in the gaming industry. I honestly can’t recommend this game enough. Did we also mention that it is free?

Alien Swarm on Steam