A world built to grow
Not a trilogy with one villain
Sphereworld is not designed as a single saga with one dark lord and one foretold ending. It is designed as a place — large enough, and deep enough in time, to hold many stories at once.
Different protagonists. Different eras. Sometimes different genres entirely: a voyage of discovery in one corner, a political intrigue in another, a quiet study of a single institution in a third. Closer to Discworld or the Culture than to one continuous arc.