Well, until I see gameplay footage and read more detail information, I'm keeping my expectations low...
If we look at the game mechanics in the existing core game we have lots of simplistic mini-games. What's to suggest Horizons will not be more of the same? We have Powerplay which IMHO is not only a mis-concieved design, it's a worryingly simplistic design with no attempt to deepen peoples gaming exerience, but simply re-offer the same limited mini-games. What's to suggest Horizons will not be more of the same?
So until I see or find out more of new mechanics offered in Horizons, I'll assume they are more mini-games bolted onto the side of more mini-games. Until I see otherwise, I will not expect a single sniff of anything deep enough to offer any emergent/deep gameplay mechanics.
I know this sounds a little cynical, but since the games release I've seen little if no sand added to the sandbox to improve core gameplay, which remains frustratingly simple IMHO. If the core game is like this, apples don't often fall far from the tree...
Fingers crossed I'm wrong, and we get wonderful new deep/broad gameplay and visuals... But I'm limiting my expectations based on current/previous experience at the moment.