There was a fairly sizable kerfuffle when Left 4 Dead 2 was unexpectedly announced. There was even a small boycott effort launched.
Gamers were mostly upset with Valve for announcing Left 4 Dead 2 before they felt Left 4 Dead 1 had reached the end of its lifespan. Many gamers saw it as a cash-in on the popularity of the game,even though Valve tried to assure people that they would continue to make content for the original game.
Another thing that miffed many was that if Valve brought out Left 4 Dead2, perceptive fans saw that this may further fractionalize and segment the game's already limited playerbase.
Valve has heard these angry Internet voices and has been trying to keep their fans happy. On the issue of splitting the playerbase, Valve now has said that they are looking at ways of allowing both Left 4 Dead 1 & 2 players to play together. The Valve team is also hoping to make it easy for mods to run on both the first and second game without much work on the part of the mod-makers.
