Great thread on Twitter talking about just this from Daniel Silvermint -
https://twitter.com/dsilvermint/stat...261136896?s=21
In short he says stories are either told by "plotters" or "pantsers." Plotters create a detailed outline to start with and then fill in the details as the story evolves. JK Rowling is a great example of a plotter; she had the whole arc of the HP novels plotted before she wrote the first one, which is why the plot points largely fit together so neatly. Pantsers on the other hand plant the seeds of the story and see where it leads them. They constantly ask themselves "what would character X do in these circumstances?" and then move in that direction with no idea where they will end up. GRRM is one of the most famous pantsers ever, and has said he hates writing if he knows in advance how it will end.
Neither style is right or wrong, but they do have distinct advantages and disadvantages. Plotters know where the story is going, which can lead characters to behave in unusual ways in order to further the overall plot. If Character X is slated for a heel turn, one way or the other you have to make that happen. Pantsers don't have that particular challenge, and as a result their characters are much more consistent and believable in their actions. However, there's no neat bow at the end to tie things up.
HBO had wonderful source material to work with on character development, but GRRM really has no idea how its all supposed to end (because it's not). So there was a shift from pantsing to plotting around the end of season 6. The directors had a number of events that they needed to plot through (finish off the knight king, battle of King's Landing, Jon finds out about his past, Klegane-gate, etc.) and the remaining story became about making those scenes happen. Adding to the problem was the large number of characters who all needed to have neat bows put on their respective arcs. The result was an obvious shift in tone that the audience picked up on. So despite the fact they were getting the Klegane-gate battle they always wanted, it felt hollow.
Best of all? He did this entire thread all without spoilers!