Another great series based on the Authurian legend is Jack Whyte's the
Camulod Chronicles. It focuses more on the military/historical angle rather than focusing so much on Merlin as a wizard, but it's another really solid, great read.
And I'll just put in my hurrah for Mary Stewart's series. I, too, started my reading of Author with that series. I still have the paperbacks of it and those will be books that I won't let go of.
Jan