Takeaway: The final story is strangely satisfying.
The High King is the last of one of the best-known Young Adult fantasy series before Harry Potter. It won the Newberry Award in 1969. This was about the same time the Lord of the Rings trilogy took off in the US (the last of the Lord of the Rings books was published in 1956).
The High King is the most like the Lord of the Rings trilogy. It has the most action; it is the most focused on large-scale battles. It is the most exciting, and up until this reading, it was my favorite of the series. It is still an excellent book, but Taran Wander is more interesting as a character study. I like the action books, but they are what is driving my reading. I first read the series first in the mid-1980s and was in its target audience.