There is a really big issue with 4 man instanced dungeons where after u kicked somebody from group in dungeon he isnt kicked from dungeon and he can troll and ruin your experience so u need to reset the dungeon and start over!
Next thing is the chest looting , i mean there needs to be implemented some thing so you can prevent ninjaing every single chest - put looting sistem on chests while in group or phaze chests for ppl inside dungeons to be just for them .
And third thing is loot from bosses , i know there is random loot drop from bosses but it needs to ensure you get at least green , but it would be prefferable blue loot from bosses so you reward players for killing bosses , this way it feels like you get nothing for your effort in dungeons.