When I started reading OP-Man I though i was gonna get into just another popular shonen.
I could not be more wrong. This manga shows from the first chapter that the reader is not gonna read about a Goku, or a Luffy, or a Naruto, Ichigo... (You know, those shonen protagonists who get gradually stronger by overcoming obstacles) Saitama is so strong that he can defeat (and utterly blow up) ANYTHING without even trying. And he is extremely unhappy because he cannot get a real challenge.
Story (9): The plot is not complicated, heroes vs monsters. It is as easy as that. What makes me
give it a 9 is something you realize soon after you start reading this manga. It is a satire. A satire of all your typical shonen stereotypes, and it is done masterfully. That is how can you get invested into a simple heroes vs monsters story in which the main character is invincible.
Art (10): Yusuke Murata is amazing. Perfect in every sense. The art is outstanding and the fights are incredible,and some of the most well-drawn combat scenes that come to my memory belong in this manga.
Character (10): You could hate Saitama as a main character and you should still give this manga a 10 in this category. Secondary characters are amazing. IMHO some of the heroes rank among the best secondary characters in shonen manga. Most of the monsters are incredibly cool and special mention to Garou, who is one of the best anti-heroes ever protrayed in a manga. Period.
Enjoyment (10): When you have a plethora of awesome heroes fighting utterly terryfing, hellish strong monsters, you really can't get enough of it.
Overall: (10): One of the very best shonen manga. It is an absolute must-read.