Story:
The premiss of the story is very interesting. A world where angels have gone crazy and demons are actually more helpfull for mankind. So a group of fallen angels, or demons, have United to save humans from angels and the so called Venus. That said, the author clearly wanted a longer series to develop his ideas. I hope he could spark some interest and got the chance he wanted to make something bigger.

Art:
The art didn't impress me. The main characters are very ordinary. Specially Satan. That said, the angels are very cool. I also liked the idea the author had for the weapons. The clothes are also boring and bland. The scenery is almost non-existant.

Character:
The only development we get is for two characters. They get to know each other. It's the start of a friendship. The past of the main character is explained, but we can't really say that there was enough development to make them charming or interesting.

Enjoyment:
All in all, it is a cool concept, but for a oneshot on its own is just pointless. It's like having only the first chapter of a very long series like Naruto or Dragon Ball.

Overall:
If you don't mind reading the first chapter of a long series that will never be completed, just go for it.