Guerrilla Games announced Horizon: Zero Dawn on the Sony E3 press conference. They gave us a couple of minutes of gameplay and the set up of the backstory. Funny thing for me is that some years ago I was talking to people who worked on the project back then and they did mention a 'red haired female main character' and an 'open world RPG'. She also apparently can (dual) wield swords or other melee weapons. However, they forgot to mention a small detail; you are fighting robot dinosaurs!

I got no further information out of them, they respected their NDA's and blew my chance of becoming a secret insider (aka internet superhero).
But seeing the world and the combat at the E3 trailer, my imagination already ran wild with further speculation about the gameplay systems. So here's some of that speculation written down:

The Tribes
She mentioned being part of a tribe and that there are others. What if this game is about managing your tribe? Take care of the tribe and it will grow and maybe you'll get some fellow tribesmen companions that can go on the hunt with you.
Perhaps you will battle with other tribes or make alliances? Setting up some defenses at your base in case another tribe tries to attack it?

Dino loot
There was that little button prompt after she killed one of the smaller mecha dino's; "search watcher". It's an RPG, so you can loot the dino's, but what will you get out of that? My guess is mechanical parts to upgrade your equipment or your tribe.
That could lead to some cool gameplay loop: I need to upgrade the turrets in my base, but I need 4 more blue cores. Only [this type of mecha dino] drops the blue cores, so let's go hunt them!

Building your own Dino
What if with those parts you could build your own custom mecha dinosaur? Give it 4 legs, some wings and a large neck, go crazy! And ofcourse you can then ride it! Fly over the world even, have some air combat.
Or you could just tame (read: insert another motherboard) the existing dino's.

I think there's a lot more to this game then just 'go around the world and shoot robots'.

You mean they don't eat the robots? :P

Yeah, this thing looks fantastic. One of the most interesting things to come out of the press conferences.

Building your own Dino

What if with those parts you could build your own custom mecha dinosaur? Give it 4 legs, some wings and a large neck, go crazy! And ofcourse you can then ride it! Fly over the world even, have some air combat.

Or you could just tame (read: insert another motherboard) the existing dino's.

My child mind's memory of Zoids wants this SOOOOO damn bad!

Researching different robot "species", hacking them and making them fight for you and of course riding them like you said...
Maybe using that rope arrow to actually grapple onto bigger robots and climbing them Shadow of the Colossus style.

But yeah, my money's on some sort of research/hacking system...

I am mainly curious how they're going to justify that world in a way that makes sense and not just "the world went under and everyone got civilization and technology amnesia".

The writing from what they've shown looks about on par with what I'd expect from the guys behind Killzone... but otherwise it does look awfully cool. I really like the character design for the protagonist, too. Reminds me of the lady Barbarian from Diablo III.

I am definitely excited for this game.

Apart from Phantom Pain it's the only other game that really blew me away so far.

At first I thought the main character was Legolas with Bloom's likeness but then, well, it wasn't!

Game has potential though, looking forward to learn more about it.

@pezen: The trailer made it seem like the game was set waaay in the future. That knowledge simply could have been lost to history, at least to the tribe the protag belongs to. I wouldn't be surprised if discovering the truth of the past ended up being a major plot point.

Isn't the game made on the same engine that Shadow of Mordor was? The camera, graphics and all seem very similar.

@raspharus: No, it's Guerrilla's own engine, previously used in Shadow Fall. Engines aren't exactly a binary matter, there's no end-all be-all engine for third person sandbox action games with a set camera.

I really like the world that they're trying to build. It kinda reminds of of Enslaved: Odyssey to the West. Man that trailer was great.

This and Fallout 4 definitely were the games that caught my eye the most. If this turns out good I just may have to get a PS4.