I like Magnificent Bastards and Chessmasters pulling off their schemes. I don't know what it is about the trope that attracts me to them, but to see characters actively manipulating others in order to further some nefarious plot and doing so with intelligence and aforethought tickles me in just the right way. A good villain makes a story, far beyond the hero who stands against him, and I like my villains to be in the same vein as Lord Vetinari.

 

I like good plot twists as well. The most recent one that I enjoyed was probably Delenda Est where Minister Black gets assassinated and it seemed like the character was going to be around for years still.

Also, I like stories where the author manages to restrain himself from going overboard. Stories that are realistic, just by using some common sense. Like I don't mind Harry discovering his lost family treasures, as long as its actually stuff you'd expect him to find. Like when I'm reading a book 5 redo, I like it when its not canon compliant, stuff is different, but not different just for the sake of being different. It has to flow smooth and nothing is forced in just because the author wants it. A proper story can essentially play itself out, and I like logical progression.

Oh, and any author who has a dark!harry without mentioning light magic once is a winner in my book.

 

The five things that really suck me into stories and that I really appreciate:

1. Conversation chemistry - not romantic chemistry (although I really appreciate that), but where the sequence feels like it's something that could be said in real life. People interrupt each other, not everyone has a witty line, the sentences aren't always overloaded with exposition, basically where the scene has enough of a human element where it feels real.

2. Realistic relationships: one of the few reasons I actually really like the early chapters of Harry Potter and the Fifth Element is the relationship between Harry and the Muggle OC Eliza. Why? Because it feels real. Not only because the two have genuine chemistry, but because it's a slow-building relationship between two characters that feels human. There's no soul-bond, there's not immediate affection, there's no immediate sex, and there are very real reasons why the relationship both works and doesn't work. Most of this relies on character building, but unlike in most fics, the relationship itself feels multi-dimensional, not the same ridiculous stereotyping of relationships that you see in so many fics (and that, ironically, Fifth Element fell victim to in later chapters).

3. Worldbuilding - the other reason I tolerate Fifth Element a lot more than I should - the worldbuilding in that story is MASSIVE. Where there is a world that is well-thought out, with a lot of intricate details tying everything together... that always impresses me and makes the experience so much more immersive.

4. Mysteries - I like stories you can't genuinely see all the endings for, and that eventually tie all the little dangling elements together into a reveal that you have to be prescient to see coming, yet ultimately makes sense in the long run (but really, anyone who's read my shit knows this).

5. Moments that evoke emotion - I've got to admit, I'm a pretty cold motherfucker most of the time, and it really takes some damn good writing to make me give two shits about any character at any time... so when a story actually manages to tug my heartstrings in some way, I'm going to be all over that fic. If you can make me feel for the characters, even if it's absolute hatred, I'm going to continue reading. If a story can make me swallow back manly tears, I'm not going to stop reading. And if the story can send a shiver of anticipation down my spine, I'm never going to forget it.

 

A well written Dumbledore. Like in Shezzas Denerian Triology.

 

Now I have to check out this Fifth Element story.

Fixed that for you.

 

Well written Ron. It's done so rarely that im often able to struggle through truly terrible stories just for it.

 

Worldbuilding. (YoR, Wit of the Raven, a budding example in Taure's Lords of Magic)

Good supporting cast - referring to those who are neither the main character nor the main character's closest friends/allies. (YoR again, Dumbledore's Army & the Year of Darkness)

Well done "squishy emotions" - romance, sentimentality, mourning, etc., that don't make you want to gag at their clumsiness. (Backwards with Purpose, Cauterize, etc.)

Good badass development - characters that progress from their canon "softness" to hardened ass kickers in a progressive, believable fashion. (HP&BWL, possibly; DAYD again - Neville)

 

Character Building for sure. It is easy to bash a character or kill them off but it is so much harder to make a character you (or most people) don't like and make them important and likeable.

Emotion. There is a fine line between tugging your heartstrings and angst. It's one of the reasons why I love Friends Or Foes, because the author manages to keep it believable and the writing makes you sympathetic. He also uses Percy as a main character and it works.

Character Development. Characters that change over time believably. This is so rare to find in fics.

I care more about the characters than the story. You can have a semi weak story and have brilliant characters and have a fic that is amazing. Without good characters, I cannot stand a story.

Oh I can go on and on in this list. A good Dumbledore... Just no character bashing. Worldbuilding, sudden twists I don't expect...

 

A fic which breaks each and every one of the potter laws. I reckon it would be hilarious.

Anyway, I like a fic where magical traditions are detailed more. JKR did a piss poor job of it.

 

Well rounded, but mysterious, characters. Characters that you may not know much about background wise but you feel like you know solely based on their actions. For example, canon Dumbledore. Until the seventh book you know practically nothing about him background wise. Basically characters that are all show and no tell.

I especially love it when you get the reason behind the character's behavior in little snippets later on and it all ties together perfectly.

Also, characters that leave you guessing. Snape is one of my favorite characters from the series simply because I had no idea whether he was good or evil.

I rarely find that in fanfiction though. :/

 

Good world building, more than anything I believes makes a story great, a world not only with the large brush strokes; but with the small details that really pulls me into a story.

Snape. A decent Snape will make the worst of fics worth it.

 

So much this. A Black Comedy & Reign of Power do this so well including some extremely awesomesauce plot twists that just make them stand one step above the other great fics.

 

A well written and interesting Tom Riddle who isn't necessarily the antagonist. This is something that really makes me happy.

 

Aspects of a story that I like is a well thought out and planned plot. As MattSilver said, I really enjoy nods at earlier arcs of the story, or something small coming up again some time later.
Also, as others have said, I like really well done dialogue, that also stays on-character speech-style, if you get me.
I enjoy stories that combine a little of everything one's (Harry's) life can have, and not just focus on a certain aspect. Like, some stories are pure action, others mystery, others pure romance etcetera. I like stories that combine them all in one single masterpiece, although one aspect can still be prominent. Naturally, the number of stories that accomplish that I can count on one hand.
I love me some Harry/Fleur. No matter how the author has characterized Fleur, a bitch, an "ice-queen", a softie under armor, or whatever, if Harry is done right the story can be hilariously lulzy, impressive, or a guilty pleasure.

I suppose the only one that can compete with Harry/Fleur for best aspect would be well-done Dumbledore. When an author can capture Dumbledore in all his awesomeness, then fuck, even if it's slash, I will read it.
A close second to Harry/Fleur and awesome!Dumbledore would be a well characterized and presented Voldemort. Something Rowling failed to accomplish, sadly.

 

I enjoy stories with good revelation moments, like in Nonjon's A Black Comedy, with Harry being outed in front of his parents/relatives. Done wrong that scene would have been a huge letdown.

 

Secret identities - and the subsequent revelations thereof, when they're written well. I love it when there are aliases, spies, secret organizations (that are actually secret!), time travel Harry or someone else who manages to keep that secret, traitors, cheaters, lovers, and all manner of lying.

Most fics can't handle two faced characters that well unless they're overpowering Harry or making it really really obvious that the other character is lying and/or hiding something. But the character development and interaction when deception of any major degree is handled well (for the Greater Good (superheroes!) or otherwise (supervillains!) is incredible.

 

Though definitely not my favourite thing to read, something that really makes me happy is when I read a fic uses a character that often gets neglected, and does it right. In so many stories Snape gets put down or acts like a creeper, but in fics like Renegade Cause or Snape-centric fics like Soul Play he is just the best to read.

Similarly, any fic that elevates characters like Draco and Bellatric out of the stock cookie-cutter cliches the fandom loves to use, my rating instantly goes up.

 

Good, indepth characterization to previously shown as shallow/cringe-worthy characters, such as a more jaded/bitter Lavender Brown post werewolf mauling.

Also, 'different' and well-written characterizations that break/discard tiresome cliches, such as Manipulative!Dumbledore, or a Stalker/BatshitCrazy!Tonks/Hestia/Luna.

"Don't worry Harry," Luna replied airily, smiling at her bundled up 'guest', "I'll just have to ward you against the nargles with this knife - the runic array looking like HP+LL4EVA is just a coincidence."

 

Stories where Harry goes to Gringotts and forgets who Griphook is.