The starting point for this codex was the mini Codex published in White Dwarf (it being the closest to current way of building an army). One thing that you may not know about the White Dwarf codex is that much of the background that was written for it was never put into the magazine due to space restrictions. There is no such issue with digital editions, so much of the background in the digital codex has never been printed before.
The rules of course, have been updated as well. All the newer Codexes contain army-specific Warlord Traits and unique items, and this Codex is no exception.
Existing players will also notice a few other changes, particularly the way Acts of Faith work with your army. There are even a few additions that other newer Codexes don’t have, such as Apocalypse Formations and Altar of War scenarios.