Story:
While the whole "saving the world" kind of storyline isn't anything new, it does it so well that it makes the reader so engrossed in the story and not want to stop reading. The switch between timelines are done so well that it hardly leaves you confused on what is going on. There are so many twist and turns in the story which makes nearly every chapter such an enjoyable read.

Art:
The art is quite detailed and even as the art was already quite good from the start, as it goes on it steadily improves. I have to say Urusawa's distinct art style definitely is growing on me as it's such a refreshing treat compared to the sea of "Moe" that is pretty common in anime and manga.

Character:
My favourite aspect of 20th Century Boys has to be the cast of characters and their development through out the story. All of them have interesting traits and everyone was given a time to shine.

There isn't much cliched character archetypes here, most of the characters act mostly realistically so no annoying tsunderes etc. One example would be Yoshitsune as at the beginning he would seem like one of those stereotypical anime characters with glasses which are usually really weak and cowardly but it turns out he was the one that really stood up for his friends and always tried to do everything to help them.

The main character, Kenji seemed like the most "normal" out of all the characters, while some people would find him boring and they'd probably like Otcho (Kenji's best friend) more but honestly there isn't anyone more suited that him to be the main character since he's the most normal and easiest to relate to.

Final Thoughts:
I saw 20th Century Boys ranked quite highly here in MAL and I'm glad I gave it a chance. It's truly a masterpiece in my eyes. It's highly recommendable and I can't even say it enough you HAVE to check this manga out. After finishing it I literally just took my time thinking about what an amazing manga I just read.

Also how can you not want to read a manga that has a villian called Friend and a homeless guy called God.