One thing I miss is when knowledge used to play a part in wether you got agro or not, knowing what is agressive to sight/sound or even "True sound" was paramount to fully exploring the world. Even those level 80 zones where few dare tread were perfectly accessable (With few exceptions and even then a bit of patience went a long way) if you had knowledge or your surroundings.

I'll always miss having a open world that felt alive.