I know how that sounds. And yes, I've played Resident Evil 4 (though, not RE5. The demo comes out on the 26th...I can't wait!). So, it's no small praise when I say this.
L4D has very little story to it. Basically, you play as one of four survivors. Francis, a tattoo-covered biker; Zoey, a college student and horror movie enthusiast; Louis, a Junior Systems Analyst in his company's IT department; and Bill, a former Green Beret and a Vietnam veteran. It doesn't matter which one you play as. They have the same abilities, can use the same weapons. There's no advantage to playing as one over the other.
As a survivor, it's your mission to...survive. You have to avoid being killed by the many MANY zombies out wandering around. There are 4 campaigns to clear, each with 7 different missions. At normal difficulty, a campaign takes about an hour or maybe a little more. The campaigns really don't have much to do with each other.
In each, you explore the city, going from safe house to safe house. Along the way you encounter the mindless zombies, hunters, smokers, boomers and the occasional tank. From time to time, the zombies will attack en masse as the horde.
It's designed primarily as a co-op game and is best played that way. The AI is really quite good though. I played with a friend of mine, leaving two computer controlled characters. I never felt like they were hindering me along the way. They were there with health when I needed it, and were pretty good shots.
It's an intense game, and actually worth the money they're charging for it. That may have been the biggest surprise for me. I'd heard so much hype that I thought that there was no way it could be that good. But it was.
It actually almost makes me want to play it online. If only to play as one of the infected.
