I'm not coherent but then again no one's listening. Not being angsty, just acknowledging that I might as well be writing a diary. Very well, this IS a diary- just one I can link people to if I ever write anything interesting.
A couple of things you should know about me and Sues- 1. I've never written one (so far as I know), and 2. I have a bit of a low threshhold for Sues, which I counter with 3. being willing to tolerate them to an extent if the world is interesting and the Sue in question does interesting things.
I really got started writing through Bionicle fanfiction, for which I am in retrospect grateful. Prior to and alongside that, I had read a bunch of fantasy, fairly indiscrimnately, and a little bit of HP fanfiction, and had written tiny chunks of writing for my fourth-grade Language Arts- those fragments being entirely derivative and generic, lacking any hint of some endemic spark or any original ideas whatsoever. Most fantasy (though hardly all), with Harry Potter as a particularly lucid example, is set around an individual, or a small set of individuals, out of which one is often the "most interesting", or the epicenter.
Such people are very easily turned into "Possession Sues" by fanfiction writers, as the authors of the fanfiction take the characters and obliterate the flaws and weaknesses they naturally possess, and, not yet content, alter their good points to fit some mad scheme that makes you wonder, as a discerning reader, why they bothered with the façade of the original character at all.
The setup also encourage canonical Sues in original fiction, because there is set one central point, about which the action revolves, or who is tossed in the action- implying, often as not, that she is directly related to the events doing all the tossing, but with the added nausea of having her innocent of the chaos of those actions. Urgh.
Bionicle, on the other hand, is merchandise-driven. It is in the best interests of the authors to create a set number of characters, and then give each one equal time and distinct powers.
Nowadays, I am ridiculously sensitized to Sues. One of the most annoying is Harry Potter himself, in the later books at least.
Let's start with the flashy. He started out as an infant who survived the attack of the Dark Lord, killing him albeit not permanently in the process, he's got angst both ancient and modern, everyone in the freakin' world knows his name before he consciously does anything, he is a natural at the flashy wizarding sport, and manages to strike a glamorous balance between his nerd friend, Hermione, and his slacker friend, Ron. That's just the first year. He can also speak to snakes, is investigated with unnerving interest by a convicted murderer who turns out to be his godfather, is favored or discriminated against by his most memorable teachers, gets picked as the illegal fourth champion in the Tri-Wizard Tournament, has a special mental connection to Voldemort, uncovers a bunch of conspiracies, is the master of a particularly challenging piece of magic at age 14, and has a very close bond to a freakin' rockstar wizard who leads his school and can be found on trivia cards.
Yet throughout these things, he mantains a human side. All that fame has downsides and upsides. Petty bullies cause him trouble, he ends up solving a number of the conspiracies through dumb luck, doing horribly stupid things, and by being near the epicenter, not because he's THAT MUCH SMARTER than everyone else, and in fact other people figure the same things out and do smarter things. He actually HAS TO study, and his mastery of the Patronus charm is forced upon him by necessity, and nurtured by a very understanding teacher. He also does take charge of these things, and makes really, really horrible mistakes, and Hermione is often right, and even Ron.
And then everythng went stupid, because the sixth book came out. And we had Voldemort, back, in the open, and sitting on his hands as regards Harry while maintaining his obsession over him, meaning that despite there being a war actively on at last, Harry is far, far more concerned with "monsters in his chest", and whether Ron might or might not hate him for finding his sister attractive. Yet he's still spoonfed what he ordinarily would figure out, because Dumbledore wants it this way, for his own utterly illogical reasons, allowing him to merely wallow in his poorly-written teenage romance, dislike of certain teachers, and bizarre obsession with the Half-Blood Prince's Potions book.
Now, his SPESHULNESS begins to warp Hermione and Ron out of whack. WHY IN FUCK would Ron doubt that Malfoy was a Death Eater? Hermione, sure. That makes sense; it looks like a repeat of the First Year Snape and Quirrel business, but REALLY HARRY YOU'RE FIVE YEARS OLDER, HAVE SEEN A BUNCH OF PEOPLE DIE, AND, OF COURSE, LIVED THROUGH BEING WRONG THE FIRST TIME. Not that she mentions that, as I recall. But Ron's generally in favor of things like that, and given that his character development is entirely in the direction of potential romantic relationships, I see no reason why he should reject it, just to make Harry look special. And now he gets to learn the SPECIAL SECRETS OF VOLDEMORT'S PAST, and how, contrary to what you might have earlier thought, he was never anything like Harry, he was an evil little kid who killed people's pets for no good reason. (given how non-glamorous Voldemort's past is, why doesn't Dumbledore widely disseminate this information? I'm not sure too many Death Eaters would remain loyal to someone that pathetic; meanwhile Dumbledore's allies would both better-understand their enemy and have the ammunition to mock him)
It gets truly disgusting in the Seventh Book, though I despise that less as it had action, and Harry actually bothering to DO something about his various problems, and Ron being right about something fundamentally useful. Harry is now a Purity Stu, who in defiance of prior characterization will walk placidly to his death. Voldemort is now a blubbering idiot. Hermione is now ruled by her emotions so that Harry can be the voice of reason as well as, per normal, the driving force behind the group. And of course, as soon as Harry changes his mind about Snape, everyone else has to as well. He figures out Dumbledore's plan, ends up with all three Hallows but doesn't care, nor does he think to try using them for something to actually benefit others, and becomes godfather to an infant, at 17 and without the faintest idea how to live on his own as either a Muggle or a wizard.
On the other hand, I can stand Sues in some works. Rhapsody, from Sympohny of Ages is an example, because I like some of the aspects of the world. Yes, she's stunningly beautiful, has powerful fire magic, and ends up with a bunch of political clout and involved in several prophecies, but she ends up having to run from her enemies at times. Her teacher, a swordmaster, can actually teach her things, despite them both being adults and her having already been trained in the art of the sword. She spends much of the books being teased by Achmed, who softens some over time but not nearly to the extent she thinks he does. Rhapsody also makes mistakes. She's suspicious of the wrong people, and doesn't draw together the clues to the correct enemies for a long time. The prophecies she's involved in are often somewhat self-fulfilling- yes, she, Achmed and Grunthor will put a stop to the F'dor, but who gives a damn if there's a prophecy, it's because Achmed has a bitter racial hatred of the F'dor, and she has the major advantage of being fireproof.
Symphony of Ages is also supposed to be a romance series as well as a fantasy series, and I think that may be some justification for the "stunningly beautiful" bits. These things combine to make her palatable, if not my favorite part of the series.