The Left 4 Dead Blog has
a lengthy post outlining details for the upcoming survival pack for Left 4
Dead, Valve's multiplayer shooter. The article includes more insights into
the extensive research Valve uses to help with game design (though only one graph
this time for you PowerPoint fans), describing how they determined the way
difficulty will ramp up over time in survival mode.
Same here. I didn't think there was enough content in the original L4D release and I don't like the idea of having to pay for more of what should have already been there. I'll probably pass on this.