I can't imagine the Dresden Files getting that bad except if Jim started hiring a bad ghost writer or loose interest in finishing and just sloppily published boring books from now on, just because his contract said that he needed to write at least 3 books more for example.
I finished the third FitzChivalry trilogy despite of that it felt like the author lost interest. The first one felt promising and I was disappointed at the last two. But I still finished them.
If I don't like a book, I just stop reading. I don't like books that are boring in my opinion, when I can't somehow relate to the characters, when the storyline doesn't interest me, when there are too many inconsistencies, when the characters act like arseholes (again in my opinion), when there is no character development.
If I don't like the characters but the story is good and intersting I read on.
If the story is boring but it has good and interesting characters, I read on.
Sometimes (but very rarely) I don't like the writing style. Either because of word choice or sentence structure, because the author looses themself in some topic in unnecessary detail I am not very interested in, or because the author constantly uses confusing descriptions that prevent me from understanding what they mean.
The latter happened to me twice. I had to stop reading because even after being halfway through the book, I had just a very vague idea about what was even happening. And even this felt just very weird and illogical to me.
So, if Jim suddenly started to write in a confusing way so that I could no longer understand what he is writing about, I think this would cause me to stop reading.
