A bit late, but here’s my first impressions of Ao no Exorcist after watching 5 episodes.
The premise of the series is that the human son of Satan is training to become an exorcist with the goal of defeating Satan. He attends a special academy, which reminds me of Hogwarts from Harry Potter, where they train exorcists. A nifty feature of this academy is that any door opened with a certain type of key will link to a set location. As an exorcist becomes more experienced, he or she will obtain more keys; thus allowing them quicker access to a larger array of locations. The principal is also interesting since the latest episode reveals his origins, hinting at the fact that things might not be what they appear to be. Plus, he transforms into a dog to walk around the academy unnoticed.
Other than that, it has all the necessary ingredients to make for a pretty good shounen series. These items consist of your typical hotheaded male protagonist who also happens to have a special power, comrades who will fight alongside him, and a setting that will allow for repeated conflicts involving battle sequences. I just hope this doesn’t turn into one of those never-ending anime since I do want to see him eventually fight against Satan.