I was very disappointed by Horizon 4 when I tried it a few months ago, for me it really didn't look as good as Horizon 3.
It might look more impressive in trailers and all, but when you really play it, you can notice a lot of issues that make it look a lot less clean than Horizon 3.
Horizon 4 is for some reason VERY aliased, I mean that's probably less of a problem in 4K, but in 1440 or 1080p it's full of aliasing to the point where every lines is shimmering, it looked like anti aliasing was not doing anything at all.
The draw distance and texture detail is also really not as good as horizon 3, and you can very often see that the ground a few meters away is very blurry and not detailed.
It just looks and feel weird, while Horizon 3 still look really nice, and in my opinion a lot better (and the game itself is imo really not as good as 3, but that's another topic, though really, that thing where you get the gold medal no matter what you do in a race is so stupid, it's like they are giving you a participation trophy so no one feel left out, and therefore there's no point in doing anything right in the game).