I finished the game yesterday evening (Yaaay!! 
) and here's a my (spoiler free) review:
Story: 10/10
It's a fantastic and really well told story. You have three fully fleshed out story arcs: Aloy's personal story, the story of the current world and the story of the ancient world. By the end everything comes together really well as one epic tale.
It's imo one of (if not the) best story I have played in an open world game. A genre that definitely has problems telling good stories.
Horizon's is however very intriguing and captivating, always keeping the player focused. Aloy, the main character, is a strong personality, she is relatable and likable. I'm going to miss her but I have the feeling we will be seeing more of her in the future...
For comparison, I would rate the main story of The Witcher 3 a 9/10 and that of Final Fantasy XV a 6/10.
Gameplay: 9/10
It's a blast from beginning to end. The machines that you are fighting are wild and ferocious and they get only more and more aggressive and epic in variety and scale. You feel like a boss once you are able to take them down like a skillful hunter and not just barely outlasting them.
The best part is: You can take them down any way you want to. There are indefinite approaches. What always holds true though: Use your brain before you get going.
I wouldn't give the game a 10/10 in the gameplay department, because there were a few game mechanics that annoyed me and that were less thought-out.
Human enemies are pretty brain-dead unfortunately and there's the inventory upgrading system that was especially annoying until the end. My pouches were always full, it was always a pain not knowing what item I could actually sell and which one was useful for an outfit or weapon later. Finding the resources to upgrade your pouches also was a pain the ass.
I would rate the gameplay of The Witcher 3 a 10/10 and that of Final Fantasy XV a 8/10.
Game world: 10/10
Horizon features the most beautifully and carefully crafted game world that I have experienced so far. It even eclipses already very carefully crafted game worlds like the ones in The Elder Scrolls: Oblivion or The Witcher 3.
The scale of Horizon's world is immense and the variety of topography and climate zones is unmatched. From snowy mountains over autumnal valleys to rocky canyons to sand dunes to lush forests and overgrown jungles, everything is to be found in this world and it all blends perfectly together in one seamless world.
And that's just the nature. The remnants of our own civilization, the mysterious machine world and several tribes of the current civilization, all with their own distinct culture, make this world truly vivid, believable and immersive.
I would rate the world design of The Witcher 3 world also a 10/10 and that of Final Fantasy XV a 7/10.
Visuals: 10/10
This is by far the best looking game that I have seen. There are of course several PC games that beat Horizon in pure tech (higher resolution, framerate, crisper textures and so on), but as a complete package, including art and overall polish, it is unmatched at this point.
You basically can expect Uncharted 4's super polished visuals on an open world scale. Something I would not have thought was possible in this generation of consoles and PCs. Also, not just because of what is technically doable, but because of the huge amount of money and time, that Sony is willing to invest in its exlusive titles. There is simply no other game company/game developer that would be willing to foot a staggering bill like that.
I would rate the visuals of The Witcher 3 a 9/10 and that of Final Fantasy XV also a 9/10.
Music: 8/10
A really nice, evocative soundtrack. Apart from the iconic and haunting title theme it wasn't that remarkable though. It did a good job accentuating the game at all times but other than the title theme no track stood out and stayed in my memory now that I think about it.
I would rate the music of The Witcher 3 a 10/10 and that of Final Fantasy XV a 9/10.
All in all, the game exceeded my expectations. I was pretty hyped about it, I have to admit, but I didn't think it would actually scratch greatness. It's now one of my all time favorite RPGs. It does not quite reach The Witcher 3's genre defining brilliance (that game remains my absolute favorite) but Horizon came pretty close and in some aspects it actually did eclipse it.
In my opinion, and that of many other reviewers, every owner of a PS4 should own this game. It's Sony's best exclusive title.
