Perryqhill
Striker
I've only ever played 3, but I imagine I'd have enjoyed the setting of the Horizon 2. I certainly think the latest game blows 3 out of the water for visuals.
It certainly seems so. I've not got a 4k tv as we're overloaded with tv's in the house which are quite recent buys, not wanting to upgrade unless one packs in so I cannot comment on the 4k stuff on the one x. I recall reviews of 3 mentioning video was enhanced for 4k on the one s though and also other things were slightly enhanced and visually it was a bit better than 2.
Forza motorsport 7 cars were also a step up visually from 3 so given horizon and motorsport come out on alternate years they've had two years since 3 was released and it certainly seems to have benefited from that.