Horizon Zero Dawn is an awesome game so far. I've no idea how long the story is, but I just made it to Meridian. However, one of the main story quests brought me to an area with monsters to kill who are level 18, and I was only level 12. So I actually high-tailed it back to the starting area of the game in order to do sidequests, because I basically hauled ass to Meridian and didn't take time to explore the wilderness. When it comes to open world games, I just want to get lost. I can already tell this game is going to keep me busy for a very very long time - I might have to juggle playing it with something else. I feel a compulsion to see every corner of the wilderness whether there's something interesting there or not.
One thing I do not like - and it's a problem with almost every open world game ever, except Breath of the Wild - is I end up turning my brain off, because I just follow the quest markers on screen. 1700 feet away... 1200... 700... almost at destination. Rinse and repeat. It's very hard for me to focus on the environment and immerse myself in the world this way, especially when the world map is loaded with icons. So, I've turned off all icons on the map except for towns/cities and collectibles. And the world is gorgeous, but I find it very very difficult to orient myself and figure out where something is without constantly opening the map to look at the auto-route to the quest destination. A minimap would help solve this issue - and it's baffling why there isn't one in this game, of all games. The world map is pretty but lacking in distinctive features to my eye. I hate to compare this to Breath of the Wild but they released around the same time and I still play BOTW to this day and it does so much so right with respect to open world game design and it's hard to not be annoyed by some of these things.
Okay, that said... I am digging the hell out of this game. It is complex, it demands patience and biding your time. And very much like Breath of the Wild I am able to crank up the volume to enjoy the ambience and the sounds of nature as I'm crouching in the grass waiting to strike. Although I'm doing a very poor job of being stealthy even on 'story' difficult. Somehow everything is able to detect me or suss me out even when I'm hiding, especially those bastard Watchers. If it wasn't for them always detecting me I'd probably not be playing on the easiest difficulty setting. Ideally I want to play on 'hard' and save 'very hard/ultra hard' for a NG+ someday, but not until I figure out how to take out a whole pack without being detected.
I really do like this game and although it has several things I don't like about most AAA open world games the positives greatly outweigh the negatives, no question.