Aku No Hana, oh boy here we go.
[Disclaimer]
The following review is based off of my thoughts, opinions and observations. You are in charge of what you consume and should you choose to read all of this you are responsible for your reaction and response. Basically, it's fine if you disagree just please be a decent human being about it.

[SLIGHT SPOILERS AHEAD]
Aku No Hana is a very dark manga, I'll first be explaining the story a bit and then break it down so that it's easier to understand.

This manga follows the story of our protagonist who is obsessed with the book Les Fleurs du Mal. This book actually plays a huge role in the progression of the plot and how it affects the chapters following it.

Story:
The story is very unique, it explores the dark nature of humans. The characters have their own perspective on life, they want to see "the other side". It starts off with the plot being introduced in the first chapter and this story is supposed to show you HOW the characters deal with the situation as the plot progresses and shows you their character development through the plot. It uses the plot for character development in the most genius way possible (I think). The amount of messed up in this manga is too much, but it doesn't overdo it. The way the protagonist does everything Nakamura tells him to do is just..painful to watch/read. It angers you, it pisses you off and makes you hate Nakamura. It did its job of pissing you off and showing you how DARK it can really be. Theres two factors which lead to a very good and entertaining story: the plot progression and execution. Aku no Hana succeeds in BOTH of these factors adding to my reason why I think the plot progression is the best I've seen. Most people really don't like how it ended but I think it's fair and for those who read it just because of how messed up it is, you're not looking at anything besides that factor. The way it ended may be "cheesy" but it makes the most sense and if it had ended any differently I wouldn't be writing a review praising it. It added new characters, more character development and gives you a SATISFYING ending. That's what I love about it, it doesn't try to be "edgy" and kill off characters for the shock factor or something, it gives it a PROPER ending. I'll now be talking about the importance of the book I mentioned in the beginning called Les Fleurs Du Mal, the way how I see it, the book influences the protagonist to look at the world in the distorted way it he sees it as and tries to look for an escape from the world while the influence being the book and Nakamura ADDS to his thirst (don't know if that's the right word) of curiousity for knowing what's on the "other side" thus making him commit the actions he does.

Characters: The characters are amazingly written, the protagonist may come off as a cliché at first but they USED the cliché and made it its own thing. The other characters are also really good! The way how they vilanize (is this even a word?) Nakamura, make you hate her and then make you feel pity for her is just a ride. As for Saeki, they also re-used the trope of "nice girl, straight a's" and make her seem more twisted than ever. She first comes off as the trope I mentioned earlier and along with her character development and how they make her go from "good girl" to "crazy psycho" in the most subtle but messed up way possible is remarkably the best character plot twists I've seen. I'm also gonna mention how good the side characters are! Side characters don't matter for the most part but they added their own little bit of personality to them too making them a well written character!

Art: The art for the manga is good but average but I didn't really care for the art, as for the art of the anime I noticed how many people dropped it after seeing the art, like, dude it's like saying "oh boy this _____ looks so ugly even though it has amazing features so I'll call it trash for the sake of being edgy!". The art in the anime ADDS to the creepy factor in this anime!!

Enjoyment: I fricking loved reading this and finished it in 3 days!

Overall, I think I went over board with theories and praising how good it is but somebody had to do it since the first people look for is aesthetic attraction and not what it's about. But seriously, it's so well written that I was pleasantly surprised because it's different, new and has uncensored boobs.