If that qualifies as "mountainous highlands" then it's certainly in the game as one of the "sub-biomes" But I don't have any issue at all with what they're showing us so far. You go from epic space battles (way more epic than any we had in Halo CE) to then down onto a Halo, just like Halo CE. While on that Halo there's a mountain of objectives and story based missions, which will take us all over the ring, inside caves, forerunner structures, banished outposts, camps and strongholds, potentially other banished ships, we'll face random patrols, and I'm assuming we will run into important and named human allies as well.
I'm just ready for this new Chief adventure already. Can't wait to see what this weapon is all about, what's up with Cortana, what goes down with this pilot, and what the Banished and the new threat, the harbinger, are up to, and where it will leave the Halo universe at the end of the game. And top of my list is Atriox. How does he come into play?