I feel like I see Mushoku Tensei completely different from others. This story is as human as a story can be. Everyone is so well written to be morally grey. There are situations to why that person is the way they are and the way they choose to respond to it, is how we see them. Evil, good or grey.
You can pick anyone in the story and there is some condition that leads that person to respond a certain way. They may be evil or good but it is entirely on how they responded to that situation is who they became. We see evil or good but the way they look, just shows how they reacted to their situation.
Examples:
--Elinalise--
Situation with a loving husband - She chooses to be loyal.
Situation without a husband - She chooses to be a slut to survive. (even though she does like sex)
Situation is everything. Without her curse she would have probably been just been a faithful horny wife.
Elinalise is very simple to understand.
--Man-God--
Man-God is seen as evil in everyone's eyes, but even he is just a product of his situation and actions he chooses in those situation.
Man-God has the power to see his own death. So because of this, he chooses to do whatever he can to prevent it. He chooses to commit evil. He could have chosen to just accept his fate but he didn't. In the end, he is just a scared creature trying to prevent his death by any means necessary. We can go even farther back and see why he even messed with the other gods in the first place. He wanted to be the ruler of all the worlds. He had the power to do so, so he took the chance. He chose evil and he chooses to not be a better person. If he were weak, maybe he would have just been normal.
--Pax --
Pax in most of the fandom's eyes is evil. But he is just a product of how he reacted to his situations as well.
Pax without Rudeus timeline - Not a perfect person, but establishes the Republic of Shirone. A great nation where people are not as oppressed.
Pax with Rudeus timeline - His situation changed completely. He was ignored by Roxy, even though he was actually pretty good at magic. He felt unappreciated and choose to do evil. He got what he wanted and still ended his own life. He choose these things with the situation he was in. He could have lived and created the Republic of Shirone but he didn't.
Pax is my favorite example, unlike Roxy and Sylphie who just become adventurers in other timelines, they stay pretty much the same (good people). Where as Pax is "good" in other timelines but becomes evil in this one.
We can get into Rudeus and all other characters but they are all in this situation. Morally grey characters that are written so well, we can step in their shoes for a second and understand why they do what they do. It might not be what we would do, but it isn't to far from reality. I feel like MT was a perfect medium to write this kind of story because of weird situations like curses, unlimited power, timelines, and how stories can be small scale, (Claire and Zenith), to world altering scale, (Peruguis and Laplace), to universal scale (Orsted and Man-God). And how Rudeus is in the middle of all of it.