This is an amazing manga. I haven't read it for a long while, but from what I remember, the story is intriguing, horrific, exciting, and all too easy to fall into, albeit strikingly similar to Trigun. It has been branded as a shoujo manga, but I would say the balance between romance, action, drama, tragedy and comedy make it a suitable read for both genders.
The art is simple yet beautiful, and she has brought life to her characters and taken the effort to draw elaborate backgrounds without distracting the focus on the characters, something most shoujo manga artists fail to do. Information flows easily from one page to the next, leaving little confusion as to what is actually happening, and you're not constantly reading lengthy internal dialogue that goes on at the rate of one sentence per page over 20 or so pages.
However, what really defines a manga over the other, is how much it makes you care for the characters. This manga definitely succeeds in doing so, and you feel all the appropriate mix of emotions for the leading duo as well as for the various side characters.
I would definitely recommend this manga to most, and eagerly await the next installment. Hopefully volume 9 will be translated soon, because you just NEED to know what happens next!