I had assumed that the change in art style back to the Old School style suits was going to be explained away as having to do with Cortana and The Created, and needing to re vert to older Tech that would less susceptible to AI intrusion, control, and influence, but after the trailer my biggest reaction is What about Cortana and The Created?
Chief's dialogue makes The Banished out to be the Big Bad and greatest threat, (If we don't defeat the Banished there won't be a Home) But Halo 5's cliff hanger was all about The Created. The conversation with the Red Hologram mentions the "The Harbinger," who I guess is Cortana? Leading up to the Trailer I had assumed the Banished would be working for Cortana. However, the hologram's dialogue just mentions that the Banished and "The Harbinger" simply share "The same goal." Just share a goal, and he doesn't call the "The Harbinger" Our Master or Our Leader or even Our Ally.
Just feels like we are missing a huge chunk of story of how we from fleeing The Created and their built up as impossible to defeat Forerunner army and almost all of Humanity's AI turning against the UNSC, to the Banished being the Big Bad who are Chief's primary focus.