Wooow what a rollercoaster of emotion this manga is!
First of all: it's not for everyone. If you want a story that makes you feel happy, makes you feel better, than this manga is not for you.
It's not a 10 because of his perfect storytelling (which is perfect indeed) nor for the beautifully written characters, this manga earns a ten also because it is not only a manga, is something more, something taht makes you reflect upon life, it's truly a masterpiece. It's a 10 as a manga, it's also more as a piece of art.
Don't be put off by it's weirdness, the first volume is the weirdest one to read because you have to get it, but than this weird manga becomes suddenly reality itself.
This manga makes you reflect upon yourself, upon life. Rarely a piece of media can show us how real life really is, and what can happen if you go down a dark path, this is reality, this is hard, depressing, but also heartwarming in a sesne. After reading Oyasumi Pun Pun you feel like you understend life better, you can learn from Pun Pun's mistakes in order not to repeat them yourself.
Amazing story
Amazing art style
Beautifully written character
You maybe won't enjoy it, but sure you will like and appreciate it