I think it's interesting to see how a story evolves over time. Martin strikes me as a guy who starts with an outline so he knows where he's going, but still hews much more towards creating really believable characters, who then don't end up fitting the outline. He's then faced with a choice of "Change where the story is headed" or "conform the characters to the outline" and chooses the former usually.
I suspect this is a big part of why the last two books are taking so freaking long to finish. He's allowed the story to sprawl much farther than he originally intended, has brought in a bunch of new characters in Books 4 and 5, and now has to have them all behave in ways that are internally consistent with the characters and environment that surrounds them. That, in turn, means he has to figure out how to maneuver them in character from point A to point Z, which probably has them cross paths with still more characters, and which in turn may shift how he has to manage that end point and whatnot.
I don't mind this on the whole. I like having satisfying plot conclusions and I think it's important to keep them firmly in mind. But I also appreciate well drawn characters. What I take issue with are the two extremes where:
1. Characters behave out of character because of the demands of the plot (e.g. Danaerys torching King's Landing last episode).
or
2. Stories which end in a deeply unsatisfying manner because the writers created characters and just kind of set them loose and had no idea where their story was going. This is particularly problematic in stories that feature mysteries or prophecies or some suggestion of "The end is going to be a big deal." It's far less of a problem in stories where everything is purely about the characters just being themselves.
I'll give three examples of this being done poorly.
A. How I Met Your Mother. The end point that the showrunners tried to reach was an end point they dreamed up before the show began, and they failed to take into account how the tone of the show and nature of the characters had changed over time to move beyond that originally envisioned ending. As a result, the ending felt like a real bait and switch and was grossly mishandled. They also fell victim to the belief that "surprise" = quality storytelling and that it's important to be shocking or surprising or to keep the audience guessing. I am SO over this trope in TV and "mystery boxes" in general.
B. Battlestar Galactica. Ron Moore spent the better part of 4 years telling everyone "The Cylons have a plan!" and building it up into some big mystery, full of prophecies and weird coincidences, and the end of the story is "LULZ God did it." Spare me the literal deus ex machina nonsense, espcially in my science fiction. This was made worse by the fact that Moore actually had no idea where he was going with the story in broad strokes. The Final Five, for example, was something he added to the story without having any clue who they'd be, and then just picked people because he thought it'd be really interesting to see what would happen with the characters if it turned out they were Cylons who didn't know it.
C. The X-Files. Don't start a massive mystery/mythology if you have no idea where you're going or how it ends.
By contrast, a show like Justified ended in an entirely satisfactory fashion, with believable endings for all of the characters, because those characters behaved in ways that were true to each of them. Plus, the show was never really about some larger metaplot. Babylon 5, on the other hand, was very much about the overarching plot, spanning multiple seasons, and it still had believable ends for its characters. To me, that show remains the gold standard for how to write believable, interesting characters and still have a deeply satisfying plot.