the biggest hope i have for the sequel is that they make the open world more interesting. They had a couple of big settlements in the game that looked great, but out in the world there was a lack of things to discover. It didn't really have what games like SKyrim or The Witcher had where you can stumble on a really interesting side mission that takes two hours and is its own separate thing.
that and better human A.I, more customisation in outfits and weapons, some more classic RPG features like building relationships and owning settlements, and more influence on the world, like the groups you get involved with just kind of end as soon as you become their leader.
great game overall though
My guess is that Guerilla had to make compromises due to the limitations of the hardware. The game is made for the base PS4, first and foremost, and the CPU is a major bottleneck. It's the reason why the scope of The Witcher 3 was scaled back. I expect Horizon 2 to have significantly higher NPC density and more complex behaviors thanks to Ryzen (possibly Zen 2).