Honestly, and it pains me to say this, but I think we've seen the best that Halo has to offer.
Halo 1-3 + ODST + Reach were just spectacular. I don't think Halo will reach those heights again.
What made Halo great were the mysteries, the grandeur, the level design, the fusion of real-world scenery mixed with ancient, unknown alien constructs. The gameplay, that 30-seconds of fun, was perfection. And the multiplayer....don't get me started on how brilliant the multiplayer was (even Bungie can't match their former selves with Destiny).
The Halos of the modern age feel stripped of mystery, the grandeur replaced with bombastic set pieces, the level designs rote, and the multiplayer adequate but missing the simple skill-based appeal of past offerings.
I don't know, I think there are times when gaming's greats need to sail to the great beyond. Maybe it's that time for Halo. I'd love for a Halo 6 to win me back, but I'm not counting on it.