i have clocked over 100+ hours into this game so far since i started, playing non stop, a huge veteran of other ARPG like grim dawn, titan quest, poe, diablo 1-3 sacred 1-3 and so on
i have noticed a few things that i would love to see in the game outside of what has been talked about, notice this is what i havent heard being discussed yet.
buff/debuff icon when using certain things, when using undisputed i get 10% dmg increase for each hit on a bleeding enemy, cannot really track this anywhere, would love more ways to track stats on your procs and skills from items you equip,
more affixes on the echoes, both benefictial and non for you, etch
- spawn more rare enemies or bosses, or this map has more roaming bosses,
- chance to spawn a quest boss in this echo,
- gain more stat or anything while taking more dmg, or so on, fun buffs and debuff to make echoes more interresting than just mf and xp
better tooltip tracking on your stats, so far it seems like increase attack speed or cast speed massively buff your dmg tooltip which can be hard to track actual dps without going to target dummy, more accurate numbers on certain things would be good :),
guiding arrow for rogues, that reminds me abit of diablo 2s version, being able to single target auto aim was so fun, loved it. there is room for such a skill
a trap class like d2s assa havent been implemented in such games in a long time, would love to see something like this, close combat fist with traps,
more fun stats to play around with for idols,
a pvp system implemented at multiplayer at some point ofcourse its very hard to balance, diablo 2 wasnt balanced, we all got one shotted, but atleast we had a way to avoid alot of the dmg, except for guiding arrow spam,
necrotic, void and poisen should have more than just another type to resist, it should have its own thing like lightning, stun / fire ignite / cold freeze,
items equipped should visually look the part, expecially legendary has a very cool look to it but some of it doesnt represent the look at all,
convert mana cost to health cost instead? somehow a stat,
loot goblin like style minions ? very fun, allways addicting to chase into a pack and die 
more stat that actually change the way you play around with that certain skill,
better pathing for hitting on stairs or teleporting/dashing through objects, at atm you kinda get stuck in enviroment and even hitting on stairs can some times block path
better responds when casting a certain spell, some times i wanna use a spell but it doesnt go off because im doing something else or casting something else, it can feel clunky when casting but then trying to pop a defensive skill just to see it not go off even though you pressed it,
better lore explaination like books or lore notes hidden around ,
i got tons more, so hit me up if you need something explained , love the direction this game is going, it has quickly become one of my favorit ARPG of this generation since D2! and i have played the others well over 100-1000+ hours