Hard to put into words but,to me at least everything seems brighter,sharper,nicer colour contrasts and schemes.All of which would have looked out of place in the Old World. The Warrior Priests photographed in the 1st Age of Sigmar book are a good example of the change.
I'm just trying to imagine how GW would paint state Troops etc in Age of Sigmar and then work something out for myself.
The Seraphon are a good example of how round bases and a new colour palette can breathe new life into an existing range and make it fit right into AoS.I'm thinking State Troops if painted in the right schemes would cross over into the AoS world rather well.