Definitely Not A Cop said:
I think what Sanderson is doing right now is incredible. I really can't think of another author who has attempted something like this with multiple different series being all interconnected, besides Stephen King.
I much prefer Sanderson though.
Let me introduce you to my friend Raymond E. Feist. His Riftwar Saga is 10 complete series with different characters, timelines, settings, and even scale. Some are focused on young teenagers and their plights as they discover the harsh world around them to entire species involved in planet ending (literal) wars. His series can be treated as standalones in their own regard but all tie into and contribute to the overall arc as well. It is always building. Until the last 2 or 3 series in which he starts to culminate everything into the grand finale.
I am a fan, case you haven't noticed.
https://en.wikipedia.org/wiki/The_Riftwar_Cycle