In the end, Ged recognized the Shadow as the dark part of himself, and absorbed it, thus defeating it. But that concept created some strange waves in the story's plot. Aren't, then, all the Nameless Ones logically the same thing? The dark sides of other people of Earthsea? Ged mentioned that a part of him had been missing, but he'd found it again. And yet, when the Nameless Ones are released, that concept is lost again. They seem to be ravaging monsters only, rather than aspects of the people of Earthsea..aspects they must accept to conquer, just as Ged did.
I tried to piece together the story at the beginning of the series, using the knowledge we glean at the end, again, that the Nameless Ones are the dark side of humanity. The Amulet of Peace, then, somehow allowed people to suppress their dark sides, and eventually after the Amulet was destroyed, the priestess' faith imprisoned the Nameless Ones. But looking at that priestess who was out to kill the Reverend Mother, as well as the conquering King Tygath, it seems clear that humanity is just as dark without its dark side, indeed with its dark side imprisoned behind a pair of really big doors. Shouldn't the warmongering Tygath be impossible so long as the Nameless Ones are imprisoned? Or perhaps only some of the Nameless Ones were imprisoned, and others returned to their hosts, devouring their souls in evil...?