The first time I saw Horizon Zero Dawn was within E3 itself. Most of us know that there wasn't much shown besides that this game happens in the distant future after what appears to be a robot revolt that almost wiped out human civilization.
This year's trailer supplements what we already know. We play as a young woman named Aloy, exploring a wilderness full of mechanical creatures. A wide selection of tools is provided to the player in hunting down these machines to harvests their components. Combat appears to be more tactical than most other shooters. Some mechanical creatures are weak to certain elements such as fire. Some have weak spots that Aloy can exploit for quick takedowns.
We are now given a brief story background, which includes a other mechanical creatures "corrupting" other mechanical creatures, thus turning them aggressive. Of course, that's just an ancient and cooler way of saying; these bigger robots are uploading viruses or malware to these smaller robots.