This is an astonishing piece of work. The complexities of Filius and Griphook are exquisitely rendered here. And the willful blindness Neville seems to show--the way he doesn't even credit Goblin heritage as having traditions that are meaningful, critical to the Goblins--shows so much why Goblins won't trust or respect wizards.
The ways Filius and Griphook interact as well--that Griphook outs Filius, and doesn't resent but despises Filius for choosing to "pass" as a wizard--they are so real, true to life. I think.
Plus there's the sex-like-coming-home, in which home is a place more violent and vivid than where you have been living.