SPOILER ALERT!
Reading progress update: I've read 475 out of 1060 pages.
So, what I don't understand about Arya is this: at this point she's pretty much driven by her desire for revenge, because that's all that's left to her (she thinks). She wants to become a Faceless Man because she thinks that the House of Black and White will train her to be a killer, so she can avenge her family. And here's what's bothering me: if you have to give up your identity in order to become a Faceless Man ... wouldn't that include giving up any feelings of revenge you might have had in your life prior to joining the House of Black and White? So why does she want to join them so badly? Or doesn't she realise that? I'm slightly confused on that point ...