The campaign is the only thing of real substance in Diablo 4.
I need a campaign that is not just a prelude, but the core of the game. I would also rather reduce the amount of side quests and integrate them as story elements that deepen the Diablo lore as stronger quest lines.
If the game is split up in such a way that you start to reel off work rather than play a game, then it’s not particularly fun, as is currently the case in D4.
The main quest is the centerpiece and the game should work like a D2 in itself and from a single source.
Therefore, a kind of working world after the story is a bad idea. Let the story + the new kind of lore quests and class quests be the actual game.
I don’t like this kind of content that you can’t just play in the world like in D2. I always have the feeling that I’m doing a job and that I have to complete it precisely, which is no fun for me at the moment, as in D4 once again.
In Diablo 2, I just went for it and always had more fun.
That’s why I say create a world without seasons, leave gates, portals, seals, walls, thorn bushes etc. closed for the time being and gradually release this content until an add-on that continues the story.
Make the classes deeper and the skill more complex. Build this on further quest lines, let the character specialize in his skills via the Paragon system.