It’s been one year since Valve released Alien Swarm for free on Steam. A remake of the original Alien Swarm developed on UT2K4, it was developed by Valve, together with the original developers, working at Valve. Originally developed as a Source mod in 2005, Alien Swarm: Infested vanished in late 2007. In July of 2010, it finally reemerged.
Its only official campaign is Jacob’s Rest. Valve has released no other levels or campaigns for the game, but modders have created numerous custom campaigns. The game is still completely free, so you can install it right now and start playing.
If you’ve already played Jacob’s Rest to death, why not pick up some fan-made campaigns? This Spring 2011 mappack has been put together by the fans themselves, featuring over 40 fan-created maps.
In conclusion, I’d probably say something cheesy like “let’s bring Alien Swarm back from the dead”, but the time spent writing that plus the time you spend reading it would be time wasted that could be spent on… well, playing Alien Swarm!