Writing this review pains me a little.
Throughout most of me reading this series, I was ready to add it to my favourites; But then, it rushed to a sudden halt.
Unfortunately this series was axed.
If you're the sort of person that can enjoy the journey despite the destination, then I think you'll definitely enjoy this manga. Otherwise, perhaps it's better to give it a miss.
Well then:

Story: 7
An achronological and fascinating mystery, there's hardly a wasted moment. It never particularly tries to moralise anything or force something down your throat, but rather the characters simply have their own (often obscure) goals. In this respect despite being in many ways "inhuman", it's a very "human" story.

Art: 9
I can see how some people might not like the art style. Unlike more popular art styles, Sekisei Inko is quite realistic. The characters also have some pretty big lips. They grow on you (metaphorically; not the lips themselves, this isn't a cursed tome, it's a manga I promise you).
In contrast to the usual realism, one character called "Memory" is rather stylised. And stylish.
It's all very beautiful. With regards to the character art, intense emotions are captured well, as well as the more quiet, sombre moments. Backgrounds tend towards realism, though most of the time the focus is on the characters.

Character: 9
There's little I can say without spoiling things. Many of the characters are filled with mystery, particularly the protagonist. He struggles with identity issues relating to his amnesia, and a big part of the series is him trying to work out who he is, what has transpired, and what other's intentions are.

Enjoyment: 7
The rushed ending really took the wind out of me. The trip however was a fun one. A bit like enjoying an amusement ride but then being kicked in the squishy bits by the operator as you hop off.

Overall: 8
I was really tempted to give this a lower score, but I wanted to stay objective about this, since it had so much value up until a certain point. The story, art, characters, and enjoyment are all 10's for me up until everything got crammed into a space the breadth of a shoe-string.
I can't imagine any of the shortcomings are the fault of the mangaka, but rather from the misfortune that the manga didn't garner enough popularity.