I think they got the casting of young Ned badly wrong. They managed to put the same terrible wig on him but it felt like amateur hour otherwise. They should have just brought back Bean instead and put some makeup on him. It's far from a perfect solution but it would have been more believable than seeing some scrawny, squinting kid with a completely different face, and it would have given this season a bigger appeal on the whole.
I'm not feeling season 6 so far. Arya's storyline is stalling. So's Dany's. And Jon's. It took them three full episodes to finally get him on his feet and push him out the door from the Night's Watch when it chould have been done in one. Even Tyrion is boring right now.
This is the weirdest thing about Game of Thrones. Martin has been criticised for over a decade for his unfocused writing, with stories going nowhere and peripheral characters eating up too much time and space, and then they go and repeat the exact same mistakes on the show. They did drop a few bad subplots last season, but the bits of story they added themselves in return were unequivocally terrible. Moreover, after five full seasons they should have figured out the pacing by now, and they should have learned how to handle multiple storylines without making every episode feel disjointed.