If the curve is too flat, then average teams will have a good experience, but really good teams can grind on long enough to cross the line from having fun to just getting worn out. There isn't enough variation in the times to separate great teams from average ones.

If the curve ramps up too sharply, we find that teams of all skill levels tend to hit a wall at the same time. We need all of these variables to work together to create a fairly smooth difficulty curve. We have numerous variables to work with: mob spawn frequency, special infected spawn frequency, number of each type of special infected, total number of special infected, tank spawn frequency, total number of tanks, and so on. Given the importance of pacing in Survival Mode, we need to define as precisely as possible how the difficulty ramps up during the course of a round. Everything from simply covering a reviving teammate, to making every shot count to minimize reloads becomes crucial in Survival Mode. It rapidly hits a fever pitch that only a well coordinated team will be able to successfully survive. Survival Mode draws on the planning and communication aspects of a successful Finale or Crescendo event, while taking it to another level.

Our goals for Survival Mode are to deliver a mode of play distinct from Campaign or Versus, have games that regularly last under ten minutes, and emphasize competition with team play through leaderboards. Survival Mode, which will be released next week, is actually a bit more than that. Just trap the survivors in a small part of a map, unleash the hordes, and record the longest time. Survival Mode pits your team against never ending waves of infected. Surviving the L4D Survival Pack ApKerry Davis and Scott Dalton

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