This is purely, 100% about Istaria...
I hate the lack of content. I hate the lack of population available to form groups for the big hunts (not the quality of the current population ). I hate the lack of rare things to collect due to their removal from the game or a dev's OCD for making things attuned. I hate waiting 6 months for an update. I hate the lack of live events that used to make this game fun.
I'm sure I will think of more within 5 minutes of finishing this post, but that's a good start...