I've not read any books in this category before. I'm not even sure that one existed until Andre Norton wrote this one. It's a mixture of historical fiction and science fiction that puts a unique face on Arthurian literature. I was sceptical about reading this novel when I first picked it up. However, I was hooked from the first page on. It's written with such a different perspective that it grabs your attention and keeps it right through to the end. In fact, I wish she would have continued this book in a trilogy or even a series. It's that good!
In this story of Merlin, Nimue and Arthur, their characters are given an extra dimension. Merlin and Arthur are half human, half alien (of the light-good), and Nimue is of the half human and alien of the dark forces. Their struggles of good vs. evil are captivating and exciting. Kept me turning page after page.
Pick up this novel and read it. You will not be sorry you did, even if you are a fan of traditional Arthurian historical fiction. This title is out-of-print but I found it quite by chance at a yearly library book sale.