It's a slightly less super well designed fun time, with the possibility of slipping down even further. It's disappointing to me that someone who played the game seriously would miss this -- or maybe thats the problem.
I'm all okay with playing a messed up game in a little bubble of goodness, but TF2 is wonderful because, unlike say Smash, it manages to be good, generally balanced fun across a large spectrum of skill. The game isn't so rickety that I have to avoid pubs or anything. I can play with guys like Yeoz (No offense!) who aren't really good at all, while guys like me or Patito or Cow duke it out at the same time. As opposed to a game like any of the smash bros that have pretty much no consideration for anything and are just random, chaotic 'fun'.
TF2 gives both the well designed, potentially competitive gameplay AND the fun crazy pubbie gameplay and both don't need to be mutually exclusive! It's easy to ignore any crap if you just go play PUGs or something, but I think the game, from the perspective of someone who plays 'casually serious', that this stuff is damaging. Not extremely damaging, but damaging. But I am also a game design fag, so this stuff bothers me at a different, fundamental level outside of actually playing the game (so if you say you don't care or this is insignificant, thats one thing, if anyone says this is actually good game design, I'm just going to flat out drop kick you).
Anyways, TF2 is the only game I can think of where pretty much all my friends can play and have fun at different levels with each other.