If you let your Steam suck your delicious bandwidth dry today, by letting it update Alien Swarm (which is free, so you should have it by now), you’re in for a treat. A wonderful, painful treat.
Valve has added a new “Onslaught” mode which switches on AI Director (that thing that controls how and when the zombies attack you in Left 4 Dead). Now, dynamically generated swarms of aliens (based on your stress level, which the game somehow knows) wait for you in the dark. Onslaught works with any difficulty setting, making each playthrough unique. Valve has also added a new difficult level called “Brutal”, that they claim is so brutal, nobody at Valve has managed to complete the game on it. If Brutal is too easy for you, there’s also a “Hardcore Friendly Fire” mode. Full damage from everything, including turrets. Not recommended if you’re going to play with people who suck.
As a reward, there are new awards: 3 new IAF Promotion Ranks: Platinum Star, Osmium Star, and the coveted Iridium Medallion.