The very first thing I noticed was that you introduce a lot of characters very quickly. In the prologue alone, you mention 16 names: Miyuki-sensei, Haniel, Dagiel, Gabriel, Uriel, Cassiel, Lucifer, Asta the Titan, Lariel, Samael, Azrael, Raziel, Azazel, the Mother, Trizael, and Salsa. I'm sure that not all these characters are important to the main story (at least not right away), so I would recommend slowing down the introductions significantly; no reader is going to remember all these people! They may eventually get to know everyone, but if the classmate isn't important after the prologue, why name them? It adds a bit of confusion.
The angel classification system also seems to be complicated. You use 14 different terms denoting rank: Virtue, Axia, Third Sphere, Ninth Rank, Falla, Second Sphere, Fifth Rank, Archangel, Knights, Seraphim, Cherubim, Thrones, Power, and merangel in the prologue. There is little explanation given for them (except for Axias and merangels), and the average reader won't have any previous knowledge about angel classification. A bit of explanation here describing spheres, ranks, and classes would be beneficial.
I do like the basis of the story, however. It seems to be interesting from the very first episode, and I would keep reading if I weren't so tired right now. Keep writing; you're very creative