Ross Douthat writes a fantasy novel

And Laura Miller, Slate's writer on literature, critiqued the posted sample chapters.

Here's my response to Miller, posted in Slate's comment section:

First, I'm dismayed that someone would set out to write a trilogy. A real trilogy is something you discover you've written only after you've done it: three separate books, with their own complete stories, written independently, which add up to a larger story when put together. But that's rare. What mostly gets called a fantasy trilogy has been artificially gingered up to meet a form of a single story in three volumes, which is why so many suffer from "middle book syndrome," where the story just marks time for 300 pages. This is all because The Lord of the Rings was published in 3 volumes, but it's not a trilogy but a 3-volume novel. It was written as one story with no intention of being divided, so it doesn't suffer from middle book syndrome.

Second, Tolkien was hardly a tortured moralizer. He did have moral beliefs, but he didn't go around preaching them. They gradually emerge from reading his work.

Third, I wonder what you mean by "essentialist understanding." Usually "essentialist" is taken to mean "all members of this class are like this." That's not true of Tolkien's elves. You could only call them "essentially good" in the other sense in which they're broadly good, they're more good than bad, they aspire to goodness. Read the Silmarillion and you'll find plenty of elves behaving extremely badly, and a few who are evil the way that Saruman in Lord of the Rings is evil. The reason you don't find elves like that in Lord of the Rings is that the elves are chastened by their earlier experiences, the ones recounted in the Silmarillion, and aren't going to make the same mistake again.

Fourth, Miller's complaint about stories consisting of "stretches of dialog in which characters explain things to each other." She's right about that. And the popular author I find most guilty of building his books that way is Philip Pullman. His first book consists mostly of Lyra overhearing conversations that the author is writing for her benefit, though the characters holding them are just telling each other things that they already know, though they don't know Lyra is there. The whole plot is built out of Lyra learning things this way. I didn't read any further. Tolkien has only a few infodumps and they're genuinely informative to the characters they're addressed to.

Fifth, Miller is even more right about how readers won't care about your invented world unless you've invested their interest in it via character. Here again Tolkien is a model.