I think the big thing I am looking for in D4 or whatever it will be called is more depth in every aspect of the game. They dumbed down D3 a bit too much. Deeper skill system without going overboard like in POE where the skill tree can actually be quite daunting to a new player. Deeper side-kick system -- being able to have more skills, do more damage, equip more slots, so for solo players you have a whole other thing to work on -- your helper.
Deeper clan system -- give clans xp for completing weekly quests and then perks for leveling up. Perks can then be spent on bonuses/passive rewards for clan members.
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That said, the only thing I would really change for the difficulties is to make it harder to reach T6, I honestly think this progression should take months and I worry about the longevity of the game when people are farming T6 first week. I don't care how people play, I don't even care if you bot all day and fill your bag with the best gear possible because it doesn't affect me, I just want the game to succeed and be popular for years because I love Diablo.
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