What can I say this is the type of anime that has great potential but never succeeds in achieveing its promise. First I wanted to mantion that I know that the anime/manga isn't finished.
The beggining starts out great introducing the different charactors sych as the Millenium Earl and Allen Walker.The atmosphere is also great if you are into more darker shounen titles. And then everything falls short. There is barely any story and it looks like the mangaka of the magna which the anime is based on used a basic design for all the missions ( pick a group of exorcists that travels to a place and fights a random or unbeatable akuma/Noah and then go back to the headquarters).
I had high hopes for the anime and manga but was dissappointet by feeling the mangaka didnt know how to progress the story very well and the only thing that made this piece some what appealing was the great ideas he had in the beggining and the design of the characters