There's a fine line, I think, between a well-written character and a good character. A well-written character might be three-dimensional, act believably within the confines of the narrative, have compelling motivations, and even come complete with their own set of flaws and unfulfilled desires. But I think what separates such characters from truly memorable "good" characters is less-quantifiable. They carry a certain je nais se pas(sp?). Not only do you understand them, empathize with them, and possibly come to revere/loathe them personally? You possibly forget for a moment that their naught but scratchings on a piece of paper.
And good example of a good, but not necessarily well-written, character--I think--would be the main protagonist in '1984'. He's believable, flawed, and legitimately makes the reader feel for him throughout the majority of the book. You can feel the helplessness and anguish he emanates from the first paragrash, to the sense of resignation and acceptance to the very last. Within the Ministry of Love, as he endures unspeakable torture at the hands of a gleefully self-styled hypocritical madman, you can almost see his torment unfold, watch the flesh slough off of him as he survives for days on end without food, water, or even the ability to move. The hiccup comes in the second act, when he forsakes every mantra and creed he'd ever adopted, to take up a covert tryst with a young woman. It's forgivable in that the story would have ground to a halt had he not not experienced some catharsis or another. But all the same, His personage does a total double-take as he goes from a subtle-yet-docile thoughtcriminal, to something akin to a giddy and reckless schoolboy. Especially after Orwell goes to great lengths to hammer in that absolutely nothing is sacred, nowhere is safe, and nobody is trustworthy.
Conversely, a prime example of what I think is a good, but maybe not well-written, character would be the protagonist in 'Bioshock: Infinite'. I can hear the cries of perplexity and anger, now: how can a character who's entire self of self is reactionary be a good character? I say again: Booker DeWitt has a special something-or-other that separates him from the pack. He's flawed, almost abhorrently-so. He has a driving goal, that he pushes onwards to within the capacity of his ability and the environment he finds himself within. Within the narrative he's believable and sympathetic. But what pulls him above all that is, well, hard to put into words. I can only say that his character was the main reason I, after completing the game, turned off the console and sat in the dark as I ruminated the journey I just undertook. It's that sort of I-don't-know-what, I think, that pulls the wheat of a good character from the chaff of a simply well-written one.