Since I really haven't given an update in a while I figured I was a bit overdue.
Currently the first map, "The Approach", is mostly done. All that remain is the making of a small sewer-like area leading up to the safe room for the level. Some of the textures are in place. Most of the functional items are in place and working. The last two large items that remain are the VIS work that needs to be done to allow the game to compile within this lifetime, and the NAV file.
If you are familiar with L4D campaign design, no further explanation is necessary. If not, the short explanation would be breaking the world into render-able segments that don't cause your computer to have a conniption fit, and making sure all enemies and allies can navigate around the map and act appropriately (respectively).
Design change: Rather than simply allow the player to freely run around in every direction and backtrack as wanted at decision points, you will have to take an active role in deciding your difficulty. For instance, one of the first decisions the player will have to make upon entering the building the first time is whether to take the elevator or stairs. The elevator provides quicker and more trouble free access to the first panic event, however you bypass any potential goodies that might be elsewhere in the building. You take the stairs, and you find out how dangerous an elevator can be during an apocalypse and take your chances with whatever lurks deeper in the building...for better or worse.
Your decisions on which way to go, what weapons to use, and who to rescue have a great impact on both difficulty, story, and the puzzles you may face.
You are Zoey. From where you go from there...it is up to you......