The other thing that I could point out is that D2's campaign is actually fun and memorable where as D3's is a basically a boring roadblock to reaching endgame.
This is also a very common complaint when players talk about PoE. Endgame is fun as hell but getting there feels like a chore for most people.
Grim Dawn somehow managed to make a very fun campaign.
So with the idea that PoE and D3's campaigns are shit and GD and D2's are not, what would make a better/memorable/not want to fall sleep on my desk from boredom leveling experience? The only things that come to mind are gameplay and items , where it's fun even at low levels in GD/D2 but god awful untill you get set items, crafted gear, good rolls, whatever else in PoE and D3.