Keep in mind that many changes came about for Horus when he turned against the Emperor. Is it no surprise that he would adopt a completely different look than the one he had been known for? The one that is most commonly associated with the Emperor and everything he stood for?
In regards to the terminator armour and lack of vision, amongst other things. Horus is still a primarch, his sense are beyond that of any other who would be in such an armour, and he is powered by the chaos gods. Maybe he just didn't need his peripheral vision because he would be able to sense or feel anyone sneaking up on him?
In regards to the terminator armour and lack of vision, amongst other things. Horus is still a primarch, his sense are beyond that of any other who would be in such an armour, and he is powered by the chaos gods. Maybe he just didn't need his peripheral vision because he would be able to sense or feel anyone sneaking up on him?