TehCookie said:[...] I doubt anyone goes "I want to write this so horribly people will enjoy it!" [...]
I think the main difference between something beeing "so bad it's good" and something beeing crafted to be amusing out of it's sheer absurdity (aka seeming bad but actually beeing put together well) is like the difference between someone falling on his arse by accident and good slapstick comedy. Both can be amusing, but they are so for diffenrent reasons.
OT: I guess it breaks down to consistency in a lot of places. Is the world consistent? Act the caracters consistent within the rules of this world? Do the events happening seem to fit in the world? If everything that is supposed to be consistent with the universe really seems consistent it isall the greater and shocking to have something deliberatly out of place.
Edit
Also: Enjoy what you enjoy. It really doesn't matter if you like artfully crafted prose with masterfull use of language or if you prefare ham and cheese to the point of hilarity. Variety is a grat thing to behold and there is no reason to judge people for enjoying different things.