Some character interactions are great, and show a big change between this and his past life. As an example: He makes friends with a talented kid he had never met in his past life, and they become childhood friends. The kid teaches him how to fight, he teaches the kid about friendship. Great setup, right?
Then the kid leaves to go on a journey and they both decide arbitrarily to not meet again for ten years. Does the MC have any reason not to go with? No, he has no immediate plans. Do they have any reason not to meet in, say, one year? Again, no. Despite that, when they finally get the opportunity to meet up again before the ten years is up they actively avoid each other because it hasn't been ten years yet. And the only conclusion I can come to is the author has done this intentionally because they know the two's dynamic was the main draw for the series.
That isn't the only problem, though. There's a lot of... Well, I don't know what to call it other than nonsensical bullshit involved with the MC. He trains on a mountain for years that slowly strips him of his senses and makes everything miserable. The narrative bemoans this, nothing will ever be the same and some of these burdens will change who you are as a person. Then he leaves the mountain and... is unchanged. He's stronger, but they had no actual impact on his goals or mentality, as though it never happened. Well, maybe it's just a one-off. Oh, then he goes to train in a spiritual realm where time is effectively frozen. The narrative stresses how everyone who does this goes insane, and even says he goes insane multiple times before regaining his sanity. It also points out without a teacher he might just train wrong for vast amounts of time, making no progress or even getting worse. He spends 2100 years in there. He comes out, he is stronger, and again, his mentality and goals are completely unchanged, as though it never happened.
There's also this weird plot element where people always have a positive first impression of him, despite in his past life him never trusting anyone and thinking it was the rule of the world. Well, great setup, maybe it's him opening up to others as they open up to hi- Oh wait, no it's not, he has a mysterious power (which the narrative assures you is definitely not mind control) that makes people like him more when they first meet. Whatever, you can still do something interesting with it. When the MC finds out, he stresses over whether it means all his newfound friendships and connections are fake, and they wouldn't have gave a shit otherwise... and then it never comes to a head. He just kinda gets over it. He also gets an opportunity to turn the power off, he does, and it's effectively never brought up again.
The story does this over and over again. Brings up some new threat or stress that makes the MC falter... and then it just goes away, with no permanent impact on him. He doesn't change as a person. He gets a goal early on and one big threat, then that goal and threat consumes every fiber of character he has and distorts the very world around him because apparently it's the only thing that matters, fuck anything else that is even briefly considered of interest.
The narrative also likes to make a big deal out of how the MC didn't get anything out of his regression, but it's just... blatantly untrue. He has knowledge of events and people from the future that give him a leg up on the situation almost immediately. On top of that there's multiple scenarios where he is literally just arbitrarily given more power. He isn't the strongest in the world, but he's so far beyond where he started he would've been a known name in his old world by chapter twenty, and he just keeps getting stronger all the time. Everyone who tells you he isn't an OP mc and he actually risks things is lying to you. They are so caught up in what the story tells you with words that they miss what it is actually depicting to you. Even when the MC is actively betrayed he is in no real danger and just keeps going. He barely loses anything, and half the time when he does, he gets it back (or something even better!) two chapters later. The biggest loss I can think of was a porter who sacrificed himself to protect the mc... and we literally only knew the character for one chapter, and the MC never thinks about it again after that!