Valve time. That's whats going on with HL2 Ep. 3.
One month is 3 months.
One year is 2.
Etc.
Anywho, why would you want a game without a storyline? Aren't you curious about how the infection started? Or how mankind is dealing with this? In HL2 there's about 10% storyline and 90% playing the game. It could easily be the same for L4D and be an even greater game.
In L4d, they've left clues on the walls and such, explaining that it's a virus type zombie infection, and you're the immune. But the fact that it places you in 4 completely unrelated scenarios is annoying to me. I wanted them to all link together, and I wanted more then just the special infected/weapons you got in the demo. It's not really a campaign, just escape maps.
Kavinsky, you HATE escape maps. That's all they are without a storyline.
And to really play L4D to it's full potential, you need to play with an actual team, with actual friends, who actually know what the hell they're doing.
Me, Hobo, Ender, and usually either Bloodwolf or Dan would always play together. We were an awesome team. We could run through expert with no problem.