I had this problem with Aku no Hana as well where I felt like the author doesn't understand human emotion, perhaps he is cripplingly autistic and only experiences interpersonal relationships through media and stories, none of his own. As such the relationships of the characters don't come across as genuine and its hard to develop any emotional bond as the reader, which translates into the events that effect them not having the impact the author desired. Further the author blows his load in the beginning by localizing all the intensive action into the first arcs and he just bubbles out goo for the latter half and by the end he is curled in the fetal position still inside of you sleep farting at you.
We have several characters here whose motivations do not make sense in the context of the story, and we also have the case of a rule change for the vampires rendering the events of the first half null and void. It was like the author was backed into a corner or one day his editor who wanted to write a story herself called him drunk scream crying for a favor and he did it.
What saved it for me was the art, which was drawn incredibly well especially since the reference material for many of the panels in the book were non existent and had to be derived from the authors mind. Other influences that were clear are Starry Night by Van Gogh which made me keep turning the pages.
In conclusion, it was completely unoffensive like elevator music, didn't leave a lasting impact, didn't really excite me or make me feel anything, and overstayed its welcome after a while.
