I don't exactly love this series, but I'll defend it... It's about the youth, the prime of life and the old age of Ged, with a story that is suited to each of these stages. The Tombs of Atuan *was* the "amazing things he's done", or at least one of the main ones and representative of the others. I appreciate Le Guin's brevity, she doesn't labour the point of Ged moving up the wizard career ladder. Not every fantasy series needs to resemble a row of bricks on the shelf.
The last book is beautiful, short yes, but like the others, every sentence is worth reading and well crafted. Not your average fantasy which is 1000 pages and full of filler.
You'll be glad to hear there are more books in the series (which I haven't read!) and Ursula le Guin wrote many other great novels and short stories.
One of the things I like about le Guin, that makes her different from many other sci-fi/fantasy authors, is that for her the action isn't the point of the story. Her stories tend to focus on social commentary or emotional development. Action is a bit of an afterthought.
I wouldn't enjoy *only* reading books like that, but it is a deliberate stylistic choice that (imo) she executes well.
It's OK if you don't like it; not everyone has to like the same thing. I just think it's worth acknowledging that the style is an intentional choice.