Not exactly comparable but I'd say so far Horizon ate Zeldas lunch.
For me, I like games that have a high fun-to-time-spent-playing ratio. Going by everything I've seen in Horizon and Zelda, Horizon looks engaging at all times and intense when combat hits. Its fun, constantly. Well, looks it as I haven't played it.
Graphics are no comparison, its a joke really to say Zelda looks better. Horizon has a beautiful artstyle with very technically proficient graphics. Graphics that enhance the artstyle. Zelda has an okay artstyle but the tech side does it no favours. Its ugly at times. The shadowing, jaggies and lack of detail definitely hinder the overall aesthetic.
The last few Zelda games have been pretty poor and boring so this to me is the game that has to prove its worth. The combat is too simple and stale, it has a lot of ways to interact with the enemies but at its core its extremely simple. You can mess around with the AI which has that MGS like element to it, and that is awesome but it looks piss easy.
I find the Zelda games great on paper but they leave a lot to be desired when you play them, execution is lacking. Going back to that ratio I mentioned, in Zelda games you travel a lot, fight some enemies with little engagement, run some more, do some boring mini game, start a dungeon, explore it (still not really having fun), get an item, use it in a cool way, finally get some excitement going ("Oh I like the way that was used") and then continue on a long spree that has little to no enjoyment. Long periods of meandering about before arriving at a memorable moment.
What I really liked from the trailers so far in Zelda is the interactivity such as cutting a tree down to cross a river and using the shield to make traversing more enjoyable. That will help break the monotony mentioned above but I need better AI systems and engaging mini games, engaging combat and "Aha!" moments from puzzles more often.
Horizon on the other hand looks refreshing. An open world game where you are engaged just crawling around the land because the sense of danger is ever present and unpredictable with something coming out of no where and providing an intense puzzle like combat situation. As you explore, you are having fun. "Fun" in the context of being engaged. You fight a Trex and your heart is pumping (mine was watching the gameplay video).
Zelda will really need to excel in the puzzles as that is their strong suit and where they excel the most. Horizon also looks to have a narrative. Key word "a". So that also provides context for your actions, and compels you to move forward. Hopefully its good, it could be crappy but if they world is interesting you don't necessarily need a good "story" per se. Not unlike Zelda in that regard.