From what they've shown it's looking like Witcher 3 with less focus on telling the story "your way", dialogue trees appear to be more about expanding the game lore and exposition than making an impact to the story (could be wrong, but with their lack of focus on branching story paths I doubt there's much of it). Combat is almost a suped up version of Witcher 3s. Big seamless open world (no loading screens in the over world like Dragon Age Inquisition). Has in depth tactical gameplay based on weapon choices and tool crafting, partnered with an action game level moment to moment action. There's also an apparent light emphasis on gear, with many different weapons and armour that can be crafted or bought.
There's only so many RPG elements you can have before your game is an RPG. I'd say Horizon, at this moment in time with our limited information, is as much an RPG as Dragon Age Inquisition and is nothing at all like Zelda in the slightest bit.