Bungie's original plans (circa 1999) for Halo a.k.a. BLAM! were much closer to a large world like this, also with minimal guidance. The ring-world of Halo was supposed to be a large landscape, requiring you to engage in guerrilla warfare and letting you improvise your way through the game with the storyline unfolding dynamically.

I'm excited to see this project happen, I've been waiting 14 years for it!