We're glad you asked, because we really like this one. It's so hard when we realize, along with Katsa, what Po has lost when he is no longer able to see. He beats himself up over his self-pity because his Grace still allows him to see, more or less, so it's not like he's even lost anything. But Katsa reminds him, "You've lost something […] and you've every right to feel sorrow for what you've lost. […] Your Grace shows you the form of things, but it doesn't show you beauty. You've lost beauty" (38.20).
And that's why we love the ending so much. Because after wrapping things up for us and explaining what Po and Katsa intend to do in the coming months, we get a sense of closure. They're lying side by side in the cave Po used as a hiding place from Leck's soldiers, and while we know they're together and everything's pretty good, we're still aware that Po's been through quite an ordeal and we can't help but wonder if he's fully recovered.
Then Po says to Katsa, "I wish you could see this cave" (E.36), which of course she can't—and he shouldn't be able to—because it's in complete darkness. When Katsa asks him what it's like, Po replies, "It's… beautiful, really" (E.38), and we know, just as his hesitation before choosing the word beautiful indicates he knows, that he's regained his ability to see beauty once again.