This fourth volume concludes the story of Valashu Elahad. The final battles that he must fight are not so harrowing as some he has been through, although some grim events still occur. When Morjin is finally defeated, the ending is moving and thrilling - partially just because of all that the heroes have suffered through in order to get there.
A fantastic end to the series, I am strongly motivated to immediately read them all again. Zindell is, in my opinion, one of our top science fiction/fantasy authors. He's also strangely obscure - I've met few who have read his books, and it's hard to find them amongst the hundreds of inferior novels that abound.
I've also thought that in some ways the Neverness stories are an updating of Dune. In the same way, the Ea books can be seen as a modernized Lord of the Rings (or Arthur cycle). In both cases, the themes in Zindell's books are different to Herbert or Tolkien's, but the concern with things that actually matter is there.
I also love that Zindell is an almost terrifyingly humane writer, and his characters all have a great love of life, and peace, that I respect. He does, in the course of his stories, pressure them to breaking point but this just makes their victories that much more poignant. The finale of The Diamond Warrior is one of his most glorious of these, a much more positive end than poor Danlo the Wild had at the conclusion of War In Heaven (the final of the Neverness books).