Rating: 9/10 or 9.5. I can't really land, I just know it's a great game.
Only kinda about Horizon disclaimer: Before I begin, you have to realize that I compare every open world RPG to The Witcher 3, whether that's fair or not. It's impossible not to because Wild Hunt did everything required to be a complete masterpiece and a standard-bearer, and it is legitimately the only RPG (outside of Witcher 2) to come out since the '90s that made me reconsider my golden trilogy of favourite RPGs of all-time (Parasite Eve, FF6 and 7).
Anyway, let's get the "bad" out of the way first: while the story is definitely interesting, it takes a while to get going and there's a specific info dump that wasn't handled as well as it could have been. If I have a criticism of Guerrilla Games as a whole, it's that they don't always handle their narrative with much finesse, and this is coming from a massive fan of them because I adore Killzone. Killzone had a great story that was let down by how they told it, leaving out the good bits. With that said, despite the flaws of how they get their message across, it is a pretty solid plot by the end of it that takes some fun turns. It's not Witcher 3 (there it is!), but it's good.
This extends to the side-quests. Again, competent, but not extraordinary. They try to make them a little more sprawling occasionally, and sometimes they succeed admirably, but it's really not where Horizon excels, which isn't a huge deal because the game is either great or amazing in every other way. You just won't come out with any of them being better than the main quests in other games like in Witcher 3, but hey, that's a strong standard to live up to.
Horizon is basically a greatest hits of other games and this genre specifically. Off the top of my head, I see the influence of Tomb Raider, Uncharted, Monster Hunter, The Last of Us, The Witcher, and Far Cry.
Simply put, it has the emphasis on scavenging that The Last of Us has, where it ties in and becomes integral to everything you do. I had the same feeling playing the Naughty Dog game, as I do this. Obviously it has the bow play and platforming that Tomb Raider has, though maybe with less danger. It has an adventure feel like Uncharted. It's trying to do quests and whatnot like The Witcher, though this influence is probably more in seeing what CD Projekt Red did with environment. Speaking of environment, it is totally Far Cry. You even hang out in bushes all the time, and go hunting.
The best part is what you expect, the giant robot battles, which is a little Monster Hunter for sure. While I think it carves itself a good identity by combining all the elements of other games, I think this propels it to bigger heights. It really is awesome how you can tackle these fights, whether it's by tying them down or setting traps. All of the robots have different attitudes and sometimes they do things you might not expect, like lunge at you, even though they're based on an animal that doesn't do that. They give you a good combination of weapons to deal with this.
It's also a staggeringly beautiful game. They really did their research and combined different elements to make a cohesive whole. From a technical standpoint, GG is always top of the line, so that's not surprise. The music also has occasional brilliant moments, which aids your trek through this wasteland.
That's basically the game, but there is crafting which is fine, and skill trees that are pretty normal for the genre. I wish these games would sometimes have more depth in the latter regard, but oh well. It's still intriguing how you can build your character and use these abilities to tackle problems.
So yeah, it's really nice to see GG make a game that is almost universally beloved. I know it'll have its haters, but critically it is a success. Killzone was always warmly received but I meet very few people who are like me and consider it their jam.