It's honestly one of the best manga ever. If you have time, also check out Billy Bat and Pluto. Billy Bat is about to finish up, and while not as great as Monster or anywhere close to 20th Century Boys, it's amazing in its own right. Pluto is probably my least favorite of his works, but its pretty good, too
I really hope he does another series, because he's one of the best, if not the best mangaka out there