no, I come from a time when games had replayability and content :-)
It does have replayability online, offline, I wouldn't argue as much. But what game doesn't have online replayability? You're playing with different people each time so its hard for the game not to be different.
Games should have solid gameplay (if it doesn't its a bad game, no arguement), once your gameplay is solid then you introduce features and balance your curves. I feel that getting solid gameplay in L4D is not an enormous achievement and because of that it should have had more content. I have played it for a lot of hours (its a solid game) but there are definitely things that could have been easily added and balanced for the price (only 2 campaigns in versus for example).
Maybe its me but I'm getting tired of games that are released with half their content and then you're charged for what should have been there in the first place (sims 2 anyone, or spore?) and games with bugs and lacking the gameplay it should have. Maybe I was spoiled when I grew up and found the first 300 games I ever played played flawlessly. Then again I don't think thats spoiled, I think thats what you should be getting when you buy a video game. Yes I understand its harder to create games now (I teach classes on game design) but the standard is still there.
Again, I do enjoy the game, it plays well and is fun, I'm not bashing it, I just think there are a few things that could have easily been added without a ton of effort.