Arya has been on my who gives a shit list ever since book 1. I hate off-the-shelf tomboy characters and the fact she's now studying to be an assassin makes it just that much worse.
Arya's adventures in the Riverlands (and Brienne's) go virtually nowhere. The only interesting parts of Arya's whole arc so far has been Jaquen at Harrenhal and brief bits with the Hound. The assassin thing is interesting, but it's taken too long for Martin to find her something to do that's actually relevant to the story.
Posted this in the other thread, un-spoiling here.
There are basically 4 (human) factions by the end of ADWD that seem to have shit going on behind the scenes: Littlefinger, Varys & the Targaryan heir(s), whomever the Oldtown faceless man was working for, and Euron Greyjoy.
I really think that Euron is going to end up being the Big Bad for the series. We barely know anything about him, but he seems to know everything worth knowing about Westeros, the growth of magic in the world,
and Danaerys. And he's got a ship named
Silence. Littlefinger's plans are basically a land grab in comparison; if everything goes according to his plans, in a few years, he'll maybe be Lord or Regent of Winterfell, Riverrun, and The Eyrie. But no one will bow to him as King. Stannis & Melisandre, Prince Doran Martell, Cersei & the Tyrells - they haven't a clue what's going on, and will probably be the first to be wiped out in the coming showdown.
I have a feeling that Stannis is going to die horribly when Melisandre misguidedly sends him off to fight the Others with his "Lightbringer". And Davos will finally be justified in choking her to death.
And speaking of Melisandre, I have a feeling that in Winds of Winter, we'll finally find out whom she was referring to when she (and I think another Red Priest) talked about servants of the "Great Other." There have to be some humans working behind the scenes to advance the agenda of the Ice god in the world, since we see so many of the Fire god servants running around.