First off, here’s a video of prototype ideas of what Halo Reach could have been: https://www.youtube.com/watch?v=gL8-A00Pdkg. This included dynamic A.I., huge space battles, global wars, and open-world-esque levels. However, a lot of it didn’t make it to Halo Reach due to time, budget, or whatever it may have been.
Here are two things 343i have said concerning Halo 5:
“Xbox One was an opportunity to think about what stories we wanted to tell, how to tell them, and how best to push the “Halo” franchise to showcase the platform.”
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“Making a “Halo” game that runs at 60 frames per second, on dedicated servers, with the scope, features and scale we’ve been dreaming of for more than a decade, is non-trivial.”
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“Halo 5: Guardians is a bigger effort than Halo 4. That applies to the content and scope of the game, as well as the technology in what’s now a brand new and more powerful engine. Certainly there are some core elements carried over from prior games, but we’ve invested a huge effort in retooling our tech to take full advantage of the Xbox One’s hardware and ecosystem to create worlds and experiences worthy of next-gen.”
They want Halo 5 to be the Halo game they’ve dreamed of making, one that pushed the limits of the Xbox One in terms of scale, scope, features, and worlds. And considering how much they’ve talked about Halo 5’s campaign being a physically massive game, I truly think we’ll be blown away by huge environments, wars going on around you and in the background, tons of enemies on screen at once, et cetera. Maybe they’ll surprise us with boat combat.
This is why I believe Halo 5 could very well be the best Halo ever.