I would bring back tier sets, get rid of titanforging, get rid of LFR, and make raiding only two difficulties. More story telling cinematic's and rich lore. A storyline that rivals the Lich King story or better. I wouldn't change M+, but I would bring back talent points in some shape or form that feels meaningful like in classic. I would add more RPG elements and stats, less action RPG, and arbitrary RNG. I would release multiple raids at a time instead of just one linear one and make them feel handcrafted and meaningful instead of the soulless raids we have now. I would stray away from anything that seems rushed because of corporate deadlines and their partnership with Activision. I would also make the cinematics dark like the new Diablo 4 trailer and Diablo 2 or WotLK.