Methods of rationality is a harry potter fan-fiction. Luckily a lot of people (no, really, there's even been a readers meet-up) have been praising the work already so I can just quote them!
The basic idea is that Harry Potter's mother's sister, instead of marrying an abusive slob, married a professor of biochemistry at Oxford University, so when he gets adopted after his biological parents, Harry James Potter-Evans-Verres is brought up in a very loving family, surrounded by books on science and SF novels, and becomes a child prodigy in science before ever learning about magic. As a result, he sets about actually *analysing* how magic works, applying the scientific method to figuring out what's *really* going on.
The results of someone able to actually *think* walking through this world that has no real logic to it and pulling at the loose ends lead to some remarkably funny moments, like when Harry makes the Sorting Hat become unexpectedly sapient by wondering about it, or his total destruction of the rules of Quidditch, but what makes the book work is the fact that it gets this humour from *actually taking the world in which it's set, and its consequences, seriously* - and as a result it really does feel like the stakes in the story are high.
Here's a little sample of rational Harry talking on quidditch
"So let me get this straight," Harry said as it seemed that Ron's explanation (with associated hand gestures) was winding down. "Catching the Snitch is worth one hundred and fifty points?"
"Yeah -"
"How many ten-point goals does one side usually score not counting the Snitch?"
"Um, maybe fifteen or twenty in professional games -"
"That's just wrong. That violates every possible rule of game design. Look, the rest of this game sounds like it might make sense, sort of, for a sport I mean, but you're basically saying that catching the Snitch overwhelms almost any ordinary point spread. The two Seekers are up there flying around looking for the Snitch and usually not interacting with anyone else, spotting the Snitch first is going to be mostly luck -"
"It's not luck!" protested Ron. "You've got to keep your eyes moving in the right pattern -"
"That's not interactive, there's no back-and-forth with the other player and how much fun is it to watch someone incredibly good at moving their eyes? And then whichever Seeker gets lucky swoops in and grabs the Snitch and makes everyone else's work moot. It's like someone took a real game and grafted on this pointless extra position just so that you could be the Most Important Player without needing to really get involved or learn the rest of it. Who was the first Seeker, the King's idiot son who wanted to play Quidditch but couldn't understand the rules?" Actually, now that Harry thought about it, that seemed like a surprisingly good hypothesis. Put him on a broomstick and tell him to catch the shiny thing...
Ron's face pulled into a scowl. "If you don't like Quidditch, you don't have to make fun of it!"
"If you can't criticize, you can't optimize. I'm suggesting how to improve the game. And it's very simple. Get rid of the Snitch."
I can honestly say that i'm more emotionally invested in this work than I ever was in the original, that the characters are far better realised and more interesting than the original, the plot is far more complex and that i've learned more about rationality through this than any other work of fiction.science buff would love this thing (the reason why I opened the thread in this forum is because, book forum is dead.)
So, did you find it better than original work and if not, why?