In my opinion, it's just below Witcher 3. There is a lot of cool stuff in there and a lot of mystery that surrounds the area you are in. The story might be better than Witcher 3 but it doesn't have the crazy amount of world building or political intrigued. It's similar to the TV show Lost on how the island in the show was it's own mystery. Horizons is a bit like that. It's damn neat.
The only knock I have against Horizons is everything is taking from some other game. It's 75% Far Cry Primal but in a 3rd person view and fair bit sneaking. But the entire game is developed extremely well, the atmosphere is spot on and there is general sense of mystery that surrounds the setting and story. The characters are definitely not as good as anything Bioware has done though.
And the robot animals are breathtaking in my opinion. There is a fair bit of difference between them and fighting some of the more difficulty ones can be a 30 minute affairs.
Overall, it's a fantastic game but it's definitely not groundbreaking in any means.