I'm only half-kidding with the title of this post. L4D is a product which the producers sold to us as being something they were going to work on like TF2. We were expecting continuous development, and now we see there is a sequel in less than a year. (364 days exactly, which seems like a taunt to me).
This game is what we were expecting from the first game. They've fixed the problem with camping in corners, and left the original game as flawed as ever.
I didn't invent these expectations of updates. There's an interview where somebody who works on the game promises new characters, new weapons, and new game modes. We got a new game mode, flawed as it is, but I doubt we're going to get anything else we were promised.