Story: 5/10
Well, it is the "Protagonist gets put in supernatural danger, weird friend comes in to save him, boom, guess now I'm involved! What can I do? Maybe I can help you fight the supernatural, go on an adventure and meet friends along the way?!!", but personally, I don't hate it that much, you have a story to tell and 50 pages to get people to pay you to tell it, its tough. The biggest problem I have is that the story didn't seem to be going anywhere, unlike the first few chapters of Bleach for example, that already presented you the expansive potential of that universe and its characters.

Art: 8/10
Honestly, I'm a sucker for this art style, I love it. The design of the "Satan" character looks great, and the Cupid's second form too. The only thing I don't like is how the other characters' faces can be a little inconsistent.

Character: 4/10
Overall, the characters where too shallow, and that's fine in a one-shot because you don't have time to develop them, but in this particular case, you could tell they weren't going anywhere.

Overall (6/10) and conclusion:
Great art, bad characters and an OK story idea. Not much to say, but if it would have gotten a full release, it probably wouldn't amount to much fun. Not a series the world will miss.