I think OPM made some misteps. I think if the Mad Cyborg had been the next "big bad" instead of Garou, Madhouse and Natsume wouldn't have lost interest. Garou was interesting, but there were no real stakes for any of the main characters. Don't get me wrong, I think ONE did a great job of essentially making it Garou's story. He was basically the protagonist (the main character) of season 2 of the anime. Which was cool. And yes, bad guys can be the protagonist. Look it up.

But to anyone with half a brain, you could pretty much see that Garou was going to go through a redemption arc. It was just telegraphed too much for readers not to see where it was ultimately going to lead. Everyone knew that as soon as Garou ran into Saitama, he would get completely and utterly crushed. And that, at some point, Garou would realize that he doesn't actually want to hurt people cuz you could tell he was a good person at heart. And, for that same reason, Garou wasn't going to die. Because it's a comedy story, and that would have been too dark.

However, if season 2 could have been about exposing the true story behind the Mad Cyborg, we would know that Saitama COULDN'T be the one to defeat him. It would have to be Genos' fight. And the narrative weight of that fight would be huge. And we wouldn't know why the mad cyborg destroyed so many lives. And we wouldn't know why the mastermind behind the cyborg did what he did, and what he was really after. That story would have been a great deal more epic IMO.

[Speaking of which, wow, after reading the entire webcomic thus far, and seeing that ONE still hasn't done the Genos Vs. Mad Cyborg fight I'm really dissapointed. What the heck?]

Also, after the aliens showed up, I thought that there would be another alien invasion at some point. Perhaps a fleet of spacecraft that could nuke the Earth, or otherwise destroy it some cool Death Star-style. We could basically have OPM meets Star Wars. Now that would be fun. You could create all this lore around the aliens, learn about alien culture, and have several types of dilemmas that Saitama couldn't just punch his way through. And Saitam meets aliens would also create a lot of opportunities for comedy. Not every weird looking creature would be a monster. So it wouldn't be as simple as good humans vs. bad monsters.