The Farthest Shore might be my favorite of the Earthsea cycle so far. A book can have many interpretations, but for me, this is a book about depression. The young Prince Arren comes to Ged, now Archmage, with awful tidings. Magic is draining out of the world, starting in the far Reaches and moving in towards the center. The two of them must set off on a perilous quest to find what is wrong and attempt to right it.

They find whole islands gone to seed and the banality of evil, where sorcery, craft, and crops fail, and people sit around bickering and arguing about when things wrong rather than trying to fix them. Once prosperous towns are now dens of slavers and drug addicts. Mad ex-sorcerers say they traded their names away for eternal life, and even the mighty dragons have been rendered mute beasts by whatever evil is lurking.

Arren and Ged chase their enemy to the edge of the known world and into the land of the dead, where they find that a powerful wizard has torn a hole in reality to gain dominion over the living and the dead. But this sacrifice is absolutely illusory--to gain everything this necromancer sacrificed his self, and so gained nothing. Ged and Arren defeat the wizard and return over the Mountains of Pain. But Ged is no longer archmage, or any kind of mage. He is spent, his doing is done.

Le Guin has great interpretations of the meaning of her own works, and she says this is about evil, and the banality of evil, but I think it's about good, and how hard it is to live when what is good is hidden in mists.