I've been helping a friend who is making a L4D map called cold case, it is a really great mod that you can see here http://l4dmapdb.com/campaign:cold-case I've been beta testing it with a friend and i can honestly say I would prefer to play this over any valve map, it's just way better. It's non linear has multiple endings and puzzles and all sorts of jazz. Anyways he is planning to make it tell a story almost like how Doom3 did it with PDAs, needless to say this requires a lot of different people to voice act. That's why I'm posting this for anyone who is interested. You will have 1 line only and I will reject it if you sound like you are forcing it too much, try to talk natural. Also don't bother asking if you aren't at least 16 years old. Anyways drop me a message on steam if you are interested.