I see why are people disappointed. It is not because the story isn't interesting at all. It is because they are only focus on main casts. They are looking individual cast and not as whole. So, get disappointed by not getting what you expect from each cast.
Therefore, I hope you all look casts and story as whole. Then, you might start to like unless it isn't your taste. That's my opinions because there are stories that I can't understand why others like although I understand the story well. From that point on, I see that people can have totally difference taste from you. It is obvious but people sometime forget about that or can't see it.
e.g. These are low rating for me:
parasite, Kill me Heal me, Architecture 101