Since release, we've received a ton of feedback and feature requests from the Alien Swarm community. The most requested additions are more variety and greater difficulty.
With that in mind, we've added "Onslaught" mode, which introduces an AI Director that dynamically generates swarms of aliens based on several factors, such as the squad's stress level. Onslaught works with any difficulty setting and ensures no mission plays the same way twice.
Speaking of difficulty, we've also added a "Brutal" difficulty level for those of you who told us "Insane" wasn't insane enough. How brutal is Brutal? Nobody on the Alien Swarm team has managed to complete a mission on it.
If for some crazy reason Brutal is still too easy for you, there's now a "Hardcore Friendly Fire" toggle. When enabled, friendly fire deals full damage immediately, flamethrowers set teammates on fire much faster, and turrets will hurt you if get caught in their crossfire. HCFF truly tests your team’s ability to work as a elite squad. Coordinating movement and firing lines become an even more integral part of the game.
Finally, to reward the most dedicated players, we've added 3 new IAF Promotion Ranks: Platinum Star, Osmium Star, and the coveted Iridium Medallion.
Available free of charge, the game thrusts players into an epic bug hunt featuring a unique blend of co-op play and squad-level tactics. Along with the game get the complete code base for Alien Swarm that features updates to the Source engine as well as the SDK.