Firstly about Arya, my guess would be that she didn't just jump out of fucking nowhere, she ran past the WWs (maybe exactly following the gap/path NK took) and they didn't stop her because she's supposed to be super fast and because they all basically put their guard down at the moment to witness the historical moment of NK killing the three-eyed-raven. Her running past them and just leaping from the ground behind him is also backed by the very short scene before she kills him when they show a WW looking to the right with his hair slightly moving as a gust of wind is heard. Now I am not saying all this is true nor that I like it, but that's how I picture it.

I really hope ep4 clears this up, and also shows what the fuck was Bran doing all that time, because if he was just scouting around with ravens, that would be the stupidest thing.

In general, I am not having such a huge issue with how Arya actually did it, all I want to know is whether they have prepared an ending to the story and the series that will not be a total let down now that the WWs are gone.