I love Mercedes Lackey's Valdemar books. Have you read
all of them? There are so many different series set there ...
The first series I read was the Last Herald Mage series. My favorite so far is Arrows of the Queen, and I also liked the Hawk Brothers one and the Gryphon (The Mage Wars) series. She also wrote a series about elves in modern-day San Francisco that I wanted to love but couldn't get into but I will still recommend trying it.
And Madeleine L'Engle.
Years ago I read a very different-from-Valdemar fantasy series, by Piers Anthony. I don't know if he ever finished it, because it got to where I couldn't find the new volumes. I'll go look it up ...
A friend of mine loved a series by Ursula K. LeGuin, and I love Susan Cooper's The Dark Is Rising series. Modern-day Britain Arthurian series, catalogued as kids' books but I discovered them as an adult. "Modern-day" is relative now, as they date from 1965-1977.
I'm assuming you've read Tolkien and Lewis already?
I'm a retired librarian, I can't help myself.