I was already thoroughly enjoying Alien Swarm by playing it the way that the developers intended it to be played, music and all. Soon enough though, my roommate pointed out to me that there was an option in-game to choose your own battle music. I was immediately blown away that they would include something like this in the game. I hadn't bothered to go digging around in the audio options menu, so I probably wouldn't have found it at all, or at least not any time soon. At the time of this discovery, I had yet to complete the Jacob's Rest campaign, so I wanted the music I was going to add to contribute significantly to the overall atmosphere of the game. Not wanting to go through too much effort, I decided to go digging around in some of the video game soundtracks I already had on my computer and add some grim, ominous songs to create some more tension. What I have listed below is what I currently have in the game.
 

Track Listing