shift legendary powers to the skill tree. skill points give a feeling of permanence and baseline power. tying character identity to legendary effects makes your character feel empty. items should amplify their identity not define it
reduce the amount of rares that drop - when a rare drops it should be exciting
make items appropriately flavorful. in diablo 2, weapons have affixes that modify the item locally; enhanced damage, flat damage, attack speed - all increase the power of the weapon, not your character. if i'm playing a melee class, what i want is a big weapon that hits hard. that's part of the fantasy. every weapon type in d4 having the same damage values at max rank is boring, and makes it hard to determine the item's power at a glance. (granular item levels is an entire other rant)
the same goes for spell casters. i don't want attack damage on a staff (unless i'm doing some kind of melee staff build), i want to scale my power in a way that is thematically resonant. skill levels, reduced enemy resistance, increased elemental damage etc... (some of this already exists in d4 but it's diluted by other axes of scaling)
affix bloat - already been talked to death about. remove redundant affixes and add affixes that actually modify how your character plays. amulets are a good example. cooldown reduction, reduced resource cost, movement speed, etc... give meaningful gameplay changes and are exciting to see.
loot distribution rate for uniques - tying all powerful uniques to an endgame uber cycle just funnels players into a single activity. uber uniques need their drop rates increased drastically. there should be a feeling that an incredibly rare and powerful item can drop at any moment no matter what you're doing.