So we all know what we like and don't like when it comes to reading, and we've talked a lot about our likes and dislikes on the forum.  My question is, are there any exceptions to that?  Have you ever tried a story that isn't something you'd normally enjoy reading and discovered that you loved it?  Or have you ever started a story that sounded right up your alley, only to find you didn't like it?  Why?  What is it that makes or breaks the deal in those cases?
I usually don't read much fantasy, even with published fiction (Harry Potter is my major exception).  I just prefer realistic fiction.  The only way I enjoy fantasy is if it at least starts off realistic and works in the fantasy slowly, in a way that seems believable.  Harry Potter is a good example of that.  In fanfic, it's On Nightingale Hill.  At first glance, it is so NOT the type of story I would normally even click on, let alone read, but it came highly recommended, so I gave it a try and loved it!  It is VERY fantasy, but it's not AU, which helps, and it does start out in reality, with Nick as a Backstreet Boy having no clue what's up with this fantasy world he finds himself in.  And it's very well-written, which also works in its favor.
On the other hand, while I normally love medical drama, I don't like poorly-written medical drama.  Too many mistakes with story structure and conventions will turn me off, but so will too many mistakes with the medical parts.  I don't expect every story to sound like it was written by a medical professional (although you can often tell when it was), but it turns me off if I can tell the author just made a bunch of stuff up without bothering to do any research.  Enjoying fiction is all about the suspension of disbelief, and that can't happen if the medicine is completely unbelievable.