I love the way the show is done, how all the heroes enter the combat scene and lose to the big guys before Saitama shows up and ends it- giving us the ability to see the inner workings and drives of all the heroes and characters. Case in point: The Sea King foiling Mumen Rider, or Bakuzan (post Monster Cells) foiling Suiryu, or even Saitama himself foiling Snake.
Also, in Season 2, the main shift of the show turns towards the other non-Saitama heroes, giving more of an insight to them than before and really helps build the world of One Punch Man, all without sacrificing any of the awesome action or witty humor.
All in all, the show is simply sublime- my favorite show of all time.