One Punch Man isn't good because it's about how cool and strong Saitama is and how everyone wants to see him fight all day because it's so rad. I mean, a lot of people might think that way, but they're idiots.
One Punch Man is good because it treats stupidly strong characters realistically. Sometimes it's about comedy, sure, but much more than that it's about how it's lonely at the top, and how if you can solve everything easily you just end up bored out of your mind. It's also about the side characters, in a way much more than it is about the main character, and how they develop in reaction to meeting a force of nature who cares about being a hero but would rather get groceries than help his reputation.
I feel like this isekai is somehow the one that pushes it over in the same way for me. Not in the same engaging, character driven way that OPM does, but it's a similar kind of thing where the power level is so off the charts that it manages to become interesting in other ways because we already know there's no tension in the fights. It helps that the inner monologues are about gauging strength and how easy certain things would be as well. I'm sure even the super awesome toughest final boss would be a piece of cake for this dude, but the way he acts like the snake was almost a danger makes me think I might actually be interested when he says there's a fight he can't possibly win.
I guess it's a matter of scale. There's a lot of isekai where the protagonist is the coolest dude around and everything he does is the most strong and everyone wants to fellate him while he poses after slaying the new demon lord.
Yet somehow, when you bump it up a notch to the point where literally everything he does is a revolution on scale with people bringing laptops to the 1300's, where his loot makes a tavern freak out and they get a letter from the head honcho of the school for magic innovation telling them "hey if it's that guy, don't even think about it, he's too wild," somehow it's the most engaging new manga I've read in a while.
Absolutely wild.