Diablo IV Season 4 Loot Reborn is a great step in the right direction.
Diablo IV Season 4 Loot Reborn also added Affixes through Tempering.
The game was arguably in a much better state, and those that experienced Diablo III at launch already understood Blizzard would more than likely tune the game after player feedback.
But one of the most important updates, at least in my opinion, involved making Necromancer a viable class in Diablo IV.