Well, just canceled my preorder. I've been going back and forth on this for a while, but it seemed like the most rational thing to do.
Why? Because I still don't know what the hell the game is. I understand the types of missions you may embark on, but I still don't know what the story structure is going to be like. Will there be a variety of narrative-driven missions that keep you going? Or will it devolve into a loot grind where you go to a place, shoot guys, and have your ghost say something about "this happened here once."
From my time with it, I didn't see any hints of Bungie at their campaign best. Meticulously designed encounters, fun set piece moments, tactical battles, and chaotic improvisation seemed to be missing or greatly diminished. I spent more time standing behind a wall and popping a stationary enemy to watch their health bar go down, whereas the only real bullet sponges in Halo were Hunters or the handful of bosses in Halo 2 (and even those would keep you on the move). Even a Scarab boss battle would give you dozens of approaches. A Devil Walker would just sort of... sit there.
I hope the reviews are super positive and that it's an adventure worth embarking on. But for now, I can wait a couple weeks to hear the consensus. Hopefully at the worst, it just feels like a solid first act in a grand story.