Or historical fantasy, either way you want to say it. He sets up made-up worlds with some historical or mythological similarities to periods of Earth history, and then writes touching, careful, powerful stories within those frames.

His first trilogy, The Fionavar Tapestry, is pretty much his effort to prove that high fantasy in the Tolkien vein can still be done powerfully without looking derivative. It's about modern real world people who are taken to a fantasy land filled with myth and history and conflict, where they each discover their different destinies. In terms of emotional impact and epic quality, by the time the series is over it's competing with if not surpassing Lord of the Rings. But it requires a pretty broad suspension of disbelief to get past the initial sections, and the story takes a little bit to get going. Once it gets going, it's one of the best quality high fantasies I've read, and makes all the other Tolkien clones look like children playing with tools they don't understand. There are multiple sections of such epic density that I couldn't tear my eyes from the page. It's a story about finding a place in the world, about duty and sacrifice, about defying evil and living with the consequences of your mistakes. It's got Christian mythology, King Arthur mythology, and probably others but it's been a good ten years since I read it.

After that he goes on to write quieter historical fantasies, but still powerful ones. Tigana is the only other one I've read, and it is excellent. A history of family and lovers within a fantasy war, illustrating powerfully the terrible costs that war exacts on them all. Good book.