Well, I finished the manga yesterday and I need to say I'm a bit disappointed.
The beginning was awesome. I really couldn't stop from reading. It felt to me like some Horror survival games I used to play. When you go around some dark mystery place and search for things. Really similar atmosphere. but then its just got ruined. There was so many potential, really sad.
From something about vol 3 the story begins to drag and drag and there isn't such much of a development except for the characters.
There is also this feeling like the mangaka killed every character when he finished using them.
I Kinda made myself to finish reading it. very predictable.
One thing that was good is the character. I didn't really liked any of them but they felt real enough to feel the story and not only to read it.
The art was so beautiful and detailed. especially the backgrounds. I don't remember when was the last time I have seen in a manga such realistic beautiful art.
The ending was a real disaster. I was like wtf where is the sequel? this cant be the end.
And i think there should be more romance in this because it seems Ako and Teru really liked each other. what a shame nothing developed of this.

It wasn't really a waste of time, and i kinda enjoyed some parts of this. A very unique work. You won't really find something like this, But still there are better Mangas out there.