Okay is the word you are looking for when describing the story. Don't get me wrong I think is worth watching. The characters (Shion, Nezumi, the old guy..) had so much potential, but it was poorly developed in the anime. I really wanted to know more about Nezumi's life, because in comparison to Shion's, it seemed like a very deep character. Also the characters were kinda of poorly defined, sometimes they would say something and the next episode they would change their minds without explanation.
I think there is novel, I am pretty sure it has another ending with another storyline (?), so I would give it try too.
The ending was kinda shocking and out of nowhere in my opinion, and also it present some little gaps in the story. I personally didn't like Safu right off the bat, HOWEVER it made it me kinda uncomfortable the fact that Nezumi killled her on purpose... didn't he know how much would Shion hate him?
I gave it a low 6 overall
