I just realized that there are a lot of really stupid people on the internet so I'll balance the bias - answer this:
What does Left4Dead offer that Resistance 2 doesn't. (a.) Yes I'm a Resistance 2 fanboy but the question stands (b.) you probably will be sparking a debate by answering this.

I can honestly say I am in the camp that is not awestruck by Half-Life. I received The Orange Box as a gift. While overall I enjoyed the game all three parts of it. I would say it did not overly impress me. I would say the game for me was marginally above average. I would not say it was bad, but for me the replay value died once I fought my way through. For me the level structure was frustrating, and in many parts so too was the combat.

So I can see where the original poster is coming from. However I am actually positively stoked for Left4Dead. My reasons are pretty simple the game is one of my fantasy concepts. Other games include cooperative play as an after though, and not a main premise. This game has an entirely different dimension to it which makes it fresh. I have watched dozens of films that make me more excited.

I like the random event element. That keeps the play honest. When you get ambushed you really are ambushed which is a real adrenaline kick that most games lose after the first play through. I also like the fact that this kick isn't accomplished through shiftless directors cut idiocy. Which you find in games like Resident Evil such as the locked camera angle blind firing. Which while it is scary is infuriatingly cheap. I do not mind being taken off guard. I mind being handicapped.

I also like the fight and flight aspect of the game. You are neither just functioning as an exterminator, or a swarmed runner. You have to fight enough to get from one location to the next. This falls squarely between Halo action and the gate runs in Oblivion. I also like the balancing mechanic that is going to keep the difficulty at the right level. I want to be challenged, and this means the game will probably not be built around kiting or tanking.

I agree with the sentiment that Left4Dead at least initially will not be in the sales league that Little Big Planet should enjoy if the average consumer does not avert their eyes. However over the long run the game will probably pass the other. This is a preferred genre on a console with a larger install base. That will look like another solid winner as players tire of the newer mainline offerings such as Gears, and the Halo 3 expansion.

Then again I could be wrong who would have thought The Orange Box would have languished under a million sold with all the positive reviews it enjoyed. Even though it was as highly rated as both Bioshock at almost two million sold, and Halo 3 at almost eight and a half million.

A. Nobody compared R2 to L4D. The question is why was L4D hyped. Why is R2 hyped? People think the game will be good for several reasons. The most obvious reason L4D is hyped, is because the poeple who developed it have never made a bad game.

B. There is no question or point B.

Not true, the post I was focusing on was Kaz's. post 8 or 9 or something.

The Orange Box has sold much more than a million.  I think it sold 1.5 million on consoles, but the PC sales were significantly higher than the console sales...we're looking at more than 3 million total.

It's a PC game first, Valve's a PC developer first.  Don't get your undies in a bundle when I say that either...plenty of work went into the 360 port for L4D, and they promised they would release content more frequently than TF2, which is going to get content on 360 this year apparently.

Anyway, if anybody says they're disappointed with HL2, I would argue it's cause they didn't play the PC version.  It's simply designed best for it.