I thought this was a good quote about what we can expect from the game. The lead writer worked at Obsidian and was the lead writer on Fallout: New Vegas.
"One of the things we're not getting into yet but will certainly be part of the play experience is also exploring the ruins of the ancient world and finding out what you can uncover there," Gonzalez teased. "If you're a story junkie, then one of the things that is sort of tantalizing for you is that this focus device that allows Aloy to study the machines also allows her to recover data from the ancient past. So you're going to be unearthing a lot of secrets, things that other people can't even know. It's just like totally lost data out there that you'll be able to recover and start to piece together. So I think maybe the promise of discovering more about that is one of the things that people haven't had a chance to really react to." http://www.ign.com/articles/2016/06/15/e3-2016-horizon-zero-dawns-writer-answers-8-key-story-questions
He also talked about the various tribes and how they differ based on their environment.
Though the gameplay released shows a uniform environment, Gonzalez promised Horizon: Zero Dawn includes "other areas that are just super verdant, and jungles or deserts. So the people that you're running across there have obviously adapted to those environments in entirely different ways. There's a huge amount of variety out there to discover in terms of the peoples that you'll be meeting."