Rating: Loved (Hated-Disliked-Okay-Liked-Loved)
A couple years ago, I had to decide about including fanfics in my year count of books. The rule I came up with was that if the fic was longer than multiple books, and if I read it 100%, then I could include it. Until now, I've read a couple multi-book length fics, but finished none of them. Harry Potter and the Methods of Rationality, longer than the first four HP books combined, is the first one I'm able to include.
Methods of Rationality is an AU. In it, Harry Potter was raised by parents who liked him. He's also a young genius, determined to be a scientist. So, when his Hogwarts letter arrived and he attended the school, he applied a more realistic scientific mind to everything.
As interesting as that set-up is, the draw of the story quickly became Harry's relationship with professor Quirrell. Never once did it become slashy (though I wish it had), it was still such a fascinating relationship. Both characters were just so intelligent, I couldn't stop reading their interactions.
Unfortunately there was one major part I didn't like. It wasn't badly written, it made more than perfect sense for it to happen, but I still disliked it a whole lot.
[Serious, major spoilers back here. Do not read unless you have no intentions to read the fic!]
While many things in this AU fic were different than in the book, one thing that wasn't different was that professor Quirrell had Voldemort inside him. The fic made it unclear until the very end, and I had held out strong hope that he would indeed have been the probably-good person he seemed to be, but nope.
All the signs were there. I (and Harry) should have realized he was Voldemort, but neither of us did. So then, when Quirrell was killed, my love of the story went out the window. Totally unfair to the fic, but I had just liked that character so much, without him the story didn't hold me anymore. [End spoiler.]
Now's a good time to read this fic, as the final chapter was posted earlier this year -- no need to wait to learn what happens! There will be an epilogue, but the author said he wouldn't post that for a year, to give people writing fanfics on his work a chance to complete their works first.
Even if you're no longer a fan of HP (like me), this fic still works. I highly recommend it! I'm about to start reading it again, so I can see all the foreshadowing and such that I missed the first time through.