And crossover- the 'split infinity' trilogy (for me, the second trilogy set in the proton/phaseverse is better forgotten)
He is not brilliant with the technical side, though; you sort of get the idea that he considers technology as another form of magic, despite the research he has done.
Macroscope, Of Man and Manta, Ghost (better to avoid that one), Prostho plus, Space tyrant, Hard sell; he's done quite a lot of tolerable and even quite decent SF, and some things like Battle circle and Firefly that don't quite fall into either category.
But his fantasy doesn't stop at Xanth, either. There's the Incarnations of immortality series, and several freestanding, like Shade of the tree, and all his semi-fictionals, like Steppe, Geodyssy, Tatham mound, and some of these are quite recent; he never stopped writing other things to concentrate on Xanthian matters.