Author has written 1 story for Harry Potter.
I'm a fan of JK's universe - that means canon compliancy down to a T.
I love (LOVE!) the relationship between Ron and Hermione, and I love Weasleys in general so most of my 'favourites' centre on them. That said, I love Remus and Tonks as well and I even enjoy the occasional Harry-Ginny fic.
I will not deny that I'm partial to a bit of true-love smut but I also love family scenes and stories.
Dialogue and description that sounds British is of the utmost importance when it comes to my enjoyment of a fic. Even something that is otherwise stunningly well-written can have me clicking 'back' with a mention of grape jelly, sexy panties or - one of the least forgivable words of all - 'mom'. It's also good to bear in mind the time frame of the books as well as their geographical setting. All of the pre-epilogue action we get takes place in the 90s.
I tend to prefer third person limited narration, mostly because it echoes JK's style. However good writing is good writing and I will read anything that I judge as such (I'm not claiming my writing is that good at all - I write purely for fun - but I think my reading preferences are fairly discerning).