I've said it so many times it's almost become my mantra when it comes to this game: L4D (1 or 2) is all about playing with people on your friends list. Pug'n L4D matches is about an 84% set sail for fail.
That said, I've still made a fracklot of steam friends thru the persistence of pug'n garbage Versus matches despite the overwhelming majority of them being garbage. Thanks to that perseverance, I have a lot of chances to play matches with better players and L4d is so much more fun b/c of it.
The campaigns seem long enough honestly and now there's 7 official campaigns for L4D2, even if one is recycled from the first game. If they were any longer, versus matches would almost begin to encroach upon the time it takes to friggin complete a WoW raid lol.