I thought it was a good surprise. From the beginning until now people always speculated who Azor is and Arya never came close to the list. But looking back at all the seasons, she has been built up for this. There have been a lot of foreshadowing. And she has always been very stealthy. In this season she even sneaked up on Jon, which surprised him. And the library stealthy play was to show the audience just how quiet she could be, even quieter than her own drops of blood. They don't have to show you straight forwardly how she went from the room to where the NK was. The show has foreshadowed enough so that the audience could use imaginations.

It was well played. And people are just disappointed because they have always been rooting for other characters like Jon or Dany as Azor and things turned out differently.

Finally, the last straw broke the camels back
This episode was so shocking to watch
What were you expecting?
Happy ending?