It's hard for me to understand why anyone thinks this game is NOT worth $50. I paid $50 each for Crysis and COD4, both of which I enjoyed playing. In single player I got maybe 8-10hours worth of entertainment each. Didn't care for Crysis multiplayer, but invested maybe another 30-40 hours in CoD4 before moving on.
Judging from the demo alone on L4D, I can easily see myself getting 40-60 hours of game time before moving on to the next game. Although after playing for four hours last night in campaign mode with three of my friends, I already had way more fun than I did with the demo. I honestly haven't had this much glee playing a video game since ca Doom.
One complaint I did have about the demo was that I beat it a little too easily on Expert mode. Let me just say that fear was laid to rest after getting our asses handed to us on Normal mode at the final battle. We finally beat it on the third try, with two down and two to go. I was mere yards away from the boat when a hunter snatched me and a hoard mobbed me. I was left 4 dead, and I couldn't have been happier.
I pre-ordered and paid only $45, I'm happy. The 4 copies for $150 is a GREAT deal. Split that 4 ways for $38 you really can't complain! But hey, I understand if this kind of entertainment is too rich for your blood. Some people are perfectly happy eating McDonald's. I won't hate.