Most of the key components of Fable wouldn't work - you'd arrive in town looking for a wife and a property only to find that every inch of land and woman-flesh is owned by some chinese conglomerate who're spamming the chat channels selling them off by the pound. So you take on a quest to save 7 chickens from a bunch of hobbes, and while you're bragging about how you're going to do it another player arrives back in town with 7 chickens and a basket of eggs under his arm. You log off for the night unfulfilled.

It might still be great - more in keeping with the original vision of Fable where you have a functioning world that exists independantly of your character : you arrive in town looking for a quest, some farmer asks you to save his daughter from a marauding troop of bandits, you head to the pub to have a bevvy first and check out the talent but as you're on your way there you see a bunch of heavily armed warriors running off in the direction of said bandits. Do you join them? Try to beat them to the girl? Try to beat them to a pulp? Or head to the pub and forget about her? And what if you get there and find that actually those bandits are another group of players, one of whom has wooed the farmer's daughter and eloped with her to the forest - do you take her back anyway? Pretend you didn't find her? Tell the farmer the truth? Tell him you didn't find her when really you slaughtered the other players and locked the daughter in your sex-dungeon? Fun for all the (Fritzl) family. 

Kalavande:

I'd strongly dispute the theory that RPG's have fallen into darkness. WoW people can create their own character and roleplay as that character, creating a past, interests and so on. The same applies to any well made RPG. I would in fact say that it's not the games, but the gamers that have gone down in quality.

I'm not so sure I fully agree with that. To an extent the mentality of the average gamer did change, but a game designer's job is to stimulate gamers towards playing a game a certain way that is fun. Thus, if a game isn't played in a fun way, the game designer is at least partially at fault. A example is the level design of Portal, by Valve. The levels where designed to stimulate players to automatically look in the right direction to notice the solution to a puzzle. Usage of colors and lines played a big part there. If the level design hadn't done this then the objective of the game would have been the same but by many players it would have been played slightly differently. They would have spent more time looking for the solution than they do now. This isn't bad gameplay by definition but it was found that players enjoyed the game more if they didn't get 'stuck' too long.

In RPGs simular stimulation could be used to get players to actively roleplay their characters, but often this isn't being done at all. Combat is far higher on designer's priority lists. And thus the gamer is stimulated to approach the game from a statistical/tactical point of view. (Create a character that is optimised for combat, not roleplay). Even though roleplaying is still technically possible, players aren't being sufficiently stimulated to do so. This is fully the game designer's responsability.