I wonder why this manga has so many disapproving comments. Is it because there's no romance? Or because the story is fast-paced and ends in epic tragedy?
My advice to you would be; ignore the low rating and the comments. This story is pretty well laid out, considering the limited number of volumes.
The plot-line moves at a rapid rate, and the characters' personalities are developed rather superficially; but somehow, that doesn't deaden the suspense at all - I'd have to say it actually made me all the more curious, and I read all three volumes in one sitting.
If you're the kind of person who has to have everything spelled out for them over the course of several (filler) chapters, and like reading character histories and flash-backs that are laid out in tiring, long-winded detail, you will definitely dislike Diabolo. However, if you enjoy figuring things out and tying up a couple of loose ends on your own, and if you have a good imagination, you are sure to like it.
The ending was dark and morbid; but therein lies the main draw for me in this series. It doesn't try to glorify or hide the cruelty and brutality of this world...instead throwing it in the readers' faces with each ing page. It is unusually realistic for a shoujo, and I approve of how Oohashi Kaoru doesn't shrink from showing us that selfishness and jealousy are a part of human nature...as well as the primary cause of our downfall.
The art is not bad at all. I wouldn't describe it as 'beautiful', but it is clear and precise - and each character is drawn with an individual flavour which made recognizing them quite easy (That is not a strong point of most manga, I can tell you!)
If you feel like reading an supernatural action-oriented manga which delves into the human psyche (albeit in a rather shallow fashion), try this!