Just realized Autumn, you say you double post because you don't feel like multi-quoting, but just then you didn't use a quote in the second post!
Anyhow, the thing that annoyed me the most about L4D was the fact that, I played the demo for about 5 days straight, the same two levels over and over again, and when I finally got the game, it was the exact same thing with just a few more levels. No storyline like they started to make us think.. No new special infected, everything was in the demo. All the weapons, characters, etc.
The only thing that kept my interest in L4D was the custom barricade builder script I made for it. After that, all that was left was to get the achievements. Which, I just have Zombie Genocide left.
Then again, it is fun killing hordes of zombies..