For me, Arya's problem is like the old statement "Its like a dog chasing a car. What does he do when he catches it?". Arya has been working 5 years to get to specifically this point; and now that she's gotten there its hard to keep my interest where there is no clear place for her to go now.
Personally though, Bran's storyline has always been my least favorite. I've always thought that Game of Thrones is at its best when it is about real people dealing with extraordinary circumstances giving us insight into things like power, family, love, abandonment, ect. Characters like all of the Lannisters are fascinating character studies.
With that said, the mystical, magical, Warg stuff has always been kind of boring to me. Plus sending your mind into animals doesn't even seem like that interesting of a power.
And I absolutely hate that old cliché fantasy trope of having everyone who has more knowledge than the central character being vauge and mysterious and keeping them on an arbitrary need-to-know basis. Why not just come out and be clear?