Slightly off topic, but I don't get how some are saying the orange box was a good value. When it first came out, weren't the forums filled with angry valve customer who cried foul because they had already bought and played HL2 and EP1? "Valve is just forcing us to "rebuy" those games so they can charge $50 for the whole package, but I just want TF2." There's some truth to that too, because only a couple months later, valve release TF2 seperately for $20.
I only wanted EP2, but I'm glad I got the orange box. TF2 was really fun, and portal was superbly excellent. Valve would have made more money from me had they charged for each product individually.
About L4D, I think it might be overpriced, for now. But who knows how large the campaigns are? And how many new campaigns valve will release in the future. Not to mention mods and addons and feature adds a la TF2. Besides, I don't mind over paying when it comes to supporting good devs, even if that means the dev getting to buy his 2nd ferrari.