(I’ll preface this by saying that I’m not talking about a system that lets you choose how you respond to other characters. That’s one of the rpg elements that I do not want to see in a mainline Halo game)
What I mean is the neat dynamic audio Halo CE-3 (maybe ODST and Reach as well; haven’t replayed them enough) have, where dialogue changes based on gameplay outcomes. If the player keeps enough marines alive through an intense firefight, they’ll end up saying lines that would otherwise be said by Cortana or simply not said at all. It’s one of those things that makes replaying the older games so interesting, and as far as I know it hasn’t been used in any of the recent games at all. There’s no fluidity to Cortana, Lasky, or Palmer’s lines since they’re all scripted to happen regardless of other friendly ai present on the map (even worse in Halo 5 with the nonstop squad exposition). Would really love to see it come back, or at least something like it.