The story was great and had the potential to be a really good anime but it lacked the punch and the thrill of adventure and the suspense and mystery of the man behind the walls. I would have loved to see a little more adventure along the way and it would have been great if the mystery remained a secret till the end. Art was good and the characters were good too but in the end, it left me feeling dissatisfied. But it was quite enjoyable. So I will suggest you give this series a watch and see it for yourself. Loved the character of Zero.